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Green_GoodERP18_FSJ_Standard/PostgreSQL/doc/postgresql/html/monitoring-stats.html

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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>27.2. The Statistics Collector</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="monitoring-ps.html" title="27.1. Standard Unix Tools" /><link rel="next" href="monitoring-locks.html" title="27.3. Viewing Locks" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">27.2. The Statistics Collector</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="monitoring-ps.html" title="27.1. Standard Unix Tools">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="monitoring.html" title="Chapter 27. Monitoring Database Activity">Up</a></td><th width="60%" align="center">Chapter 27. Monitoring Database Activity</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="monitoring-locks.html" title="27.3. Viewing Locks">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="MONITORING-STATS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">27.2. The Statistics Collector</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="monitoring-stats.html#MONITORING-STATS-SETUP">27.2.1. Statistics Collection Configuration</a></span></dt><dt><span class="sect2"><a href="monitoring-stats.html#MONITORING-STATS-VIEWS">27.2.2. Viewing Statistics</a></span></dt><dt><span class="sect2"><a href="monitoring-stats.html#MONITORING-STATS-FUNCTIONS">27.2.3. Statistics Functions</a></span></dt></dl></div><a id="id-1.6.14.7.2" class="indexterm"></a><p>

  3.    <span class="productname">PostgreSQL</span>'s <em class="firstterm">statistics collector</em>

  4.    is a subsystem that supports collection and reporting of information about

  5.    server activity.  Presently, the collector can count accesses to tables

  6.    and indexes in both disk-block and individual-row terms.  It also tracks

  7.    the total number of rows in each table, and information about vacuum and

  8.    analyze actions for each table.  It can also count calls to user-defined

  9.    functions and the total time spent in each one.

  10.   </p><p>

  11.    <span class="productname">PostgreSQL</span> also supports reporting dynamic

  12.    information about exactly what is going on in the system right now, such as

  13.    the exact command currently being executed by other server processes, and

  14.    which other connections exist in the system.  This facility is independent

  15.    of the collector process.

  16.   </p><div class="sect2" id="MONITORING-STATS-SETUP"><div class="titlepage"><div><div><h3 class="title">27.2.1. Statistics Collection Configuration</h3></div></div></div><p>

  17.    Since collection of statistics adds some overhead to query execution,

  18.    the system can be configured to collect or not collect information.

  19.    This is controlled by configuration parameters that are normally set in

  20.    <code class="filename">postgresql.conf</code>.  (See <a class="xref" href="runtime-config.html" title="Chapter 19. Server Configuration">Chapter 19</a> for

  21.    details about setting configuration parameters.)

  22.   </p><p>

  23.    The parameter <a class="xref" href="runtime-config-statistics.html#GUC-TRACK-ACTIVITIES">track_activities</a> enables monitoring

  24.    of the current command being executed by any server process.

  25.   </p><p>

  26.    The parameter <a class="xref" href="runtime-config-statistics.html#GUC-TRACK-COUNTS">track_counts</a> controls whether

  27.    statistics are collected about table and index accesses.

  28.   </p><p>

  29.    The parameter <a class="xref" href="runtime-config-statistics.html#GUC-TRACK-FUNCTIONS">track_functions</a> enables tracking of

  30.    usage of user-defined functions.

  31.   </p><p>

  32.    The parameter <a class="xref" href="runtime-config-statistics.html#GUC-TRACK-IO-TIMING">track_io_timing</a> enables monitoring

  33.    of block read and write times.

  34.   </p><p>

  35.    Normally these parameters are set in <code class="filename">postgresql.conf</code> so

  36.    that they apply to all server processes, but it is possible to turn

  37.    them on or off in individual sessions using the <a class="xref" href="sql-set.html" title="SET"><span class="refentrytitle">SET</span></a> command. (To prevent

  38.    ordinary users from hiding their activity from the administrator,

  39.    only superusers are allowed to change these parameters with

  40.    <code class="command">SET</code>.)

  41.   </p><p>

  42.    The statistics collector transmits the collected information to other

  43.    <span class="productname">PostgreSQL</span> processes through temporary files.

  44.    These files are stored in the directory named by the

  45.    <a class="xref" href="runtime-config-statistics.html#GUC-STATS-TEMP-DIRECTORY">stats_temp_directory</a> parameter,

  46.    <code class="filename">pg_stat_tmp</code> by default.

  47.    For better performance, <code class="varname">stats_temp_directory</code> can be

  48.    pointed at a RAM-based file system, decreasing physical I/O requirements.

  49.    When the server shuts down cleanly, a permanent copy of the statistics

  50.    data is stored in the <code class="filename">pg_stat</code> subdirectory, so that

  51.    statistics can be retained across server restarts.  When recovery is

  52.    performed at server start (e.g. after immediate shutdown, server crash,

  53.    and point-in-time recovery), all statistics counters are reset.

  54.   </p></div><div class="sect2" id="MONITORING-STATS-VIEWS"><div class="titlepage"><div><div><h3 class="title">27.2.2. Viewing Statistics</h3></div></div></div><p>

  55.    Several predefined views, listed in <a class="xref" href="monitoring-stats.html#MONITORING-STATS-DYNAMIC-VIEWS-TABLE" title="Table 27.1. Dynamic Statistics Views">Table 27.1</a>, are available to show

  56.    the current state of the system. There are also several other

  57.    views, listed in <a class="xref" href="monitoring-stats.html#MONITORING-STATS-VIEWS-TABLE" title="Table 27.2. Collected Statistics Views">Table 27.2</a>, available to show the results

  58.    of statistics collection.  Alternatively, one can

  59.    build custom views using the underlying statistics functions, as discussed

  60.    in <a class="xref" href="monitoring-stats.html#MONITORING-STATS-FUNCTIONS" title="27.2.3. Statistics Functions">Section 27.2.3</a>.

  61.   </p><p>

  62.    When using the statistics to monitor collected data, it is important

  63.    to realize that the information does not update instantaneously.

  64.    Each individual server process transmits new statistical counts to

  65.    the collector just before going idle; so a query or transaction still in

  66.    progress does not affect the displayed totals.  Also, the collector itself

  67.    emits a new report at most once per <code class="varname">PGSTAT_STAT_INTERVAL</code>

  68.    milliseconds (500 ms unless altered while building the server).  So the

  69.    displayed information lags behind actual activity.  However, current-query

  70.    information collected by <code class="varname">track_activities</code> is

  71.    always up-to-date.

  72.   </p><p>

  73.    Another important point is that when a server process is asked to display

  74.    any of these statistics, it first fetches the most recent report emitted by

  75.    the collector process and then continues to use this snapshot for all

  76.    statistical views and functions until the end of its current transaction.

  77.    So the statistics will show static information as long as you continue the

  78.    current transaction.  Similarly, information about the current queries of

  79.    all sessions is collected when any such information is first requested

  80.    within a transaction, and the same information will be displayed throughout

  81.    the transaction.

  82.    This is a feature, not a bug, because it allows you to perform several

  83.    queries on the statistics and correlate the results without worrying that

  84.    the numbers are changing underneath you.  But if you want to see new

  85.    results with each query, be sure to do the queries outside any transaction

  86.    block.  Alternatively, you can invoke

  87.    <code class="function">pg_stat_clear_snapshot</code>(), which will discard the

  88.    current transaction's statistics snapshot (if any).  The next use of

  89.    statistical information will cause a new snapshot to be fetched.

  90.   </p><p>

  91.    A transaction can also see its own statistics (as yet untransmitted to the

  92.    collector) in the views <code class="structname">pg_stat_xact_all_tables</code>,

  93.    <code class="structname">pg_stat_xact_sys_tables</code>,

  94.    <code class="structname">pg_stat_xact_user_tables</code>, and

  95.    <code class="structname">pg_stat_xact_user_functions</code>.  These numbers do not act as

  96.    stated above; instead they update continuously throughout the transaction.

  97.   </p><p>

  98.    Some of the information in the dynamic statistics views shown in <a class="xref" href="monitoring-stats.html#MONITORING-STATS-DYNAMIC-VIEWS-TABLE" title="Table 27.1. Dynamic Statistics Views">Table 27.1</a> is security restricted.

  99.    Ordinary users can only see all the information about their own sessions

  100.    (sessions belonging to a role that they are a member of).  In rows about

  101.    other sessions, many columns will be null.  Note, however, that the

  102.    existence of a session and its general properties such as its sessions user

  103.    and database are visible to all users.  Superusers and members of the

  104.    built-in role <code class="literal">pg_read_all_stats</code> (see also <a class="xref" href="default-roles.html" title="21.5. Default Roles">Section 21.5</a>) can see all the information about all sessions.

  105.   </p><div class="table" id="MONITORING-STATS-DYNAMIC-VIEWS-TABLE"><p class="title"><strong>Table 27.1. Dynamic Statistics Views</strong></p><div class="table-contents"><table class="table" summary="Dynamic Statistics Views" border="1"><colgroup><col /><col /></colgroup><thead><tr><th>View Name</th><th>Description</th></tr></thead><tbody><tr><td>

  106.        <code class="structname">pg_stat_activity</code>

  107.        <a id="id-1.6.14.7.6.7.2.2.1.1.2" class="indexterm"></a>

  108.       </td><td>

  109.        One row per server process, showing information related to

  110.        the current activity of that process, such as state and current query.

  111.        See <a class="xref" href="monitoring-stats.html#PG-STAT-ACTIVITY-VIEW" title="Table 27.3. pg_stat_activity View">pg_stat_activity</a> for details.

  112.       </td></tr><tr><td><code class="structname">pg_stat_replication</code><a id="id-1.6.14.7.6.7.2.2.2.1.2" class="indexterm"></a></td><td>One row per WAL sender process, showing statistics about

  113.        replication to that sender's connected standby server.

  114.        See <a class="xref" href="monitoring-stats.html#PG-STAT-REPLICATION-VIEW" title="Table 27.5. pg_stat_replication View">pg_stat_replication</a> for details.

  115.       </td></tr><tr><td><code class="structname">pg_stat_wal_receiver</code><a id="id-1.6.14.7.6.7.2.2.3.1.2" class="indexterm"></a></td><td>Only one row, showing statistics about the WAL receiver from

  116.        that receiver's connected server.

  117.        See <a class="xref" href="monitoring-stats.html#PG-STAT-WAL-RECEIVER-VIEW" title="Table 27.6. pg_stat_wal_receiver View">pg_stat_wal_receiver</a> for details.

  118.       </td></tr><tr><td><code class="structname">pg_stat_subscription</code><a id="id-1.6.14.7.6.7.2.2.4.1.2" class="indexterm"></a></td><td>At least one row per subscription, showing information about

  119.        the subscription workers.

  120.        See <a class="xref" href="monitoring-stats.html#PG-STAT-SUBSCRIPTION" title="Table 27.7. pg_stat_subscription View">pg_stat_subscription</a> for details.

  121.       </td></tr><tr><td><code class="structname">pg_stat_ssl</code><a id="id-1.6.14.7.6.7.2.2.5.1.2" class="indexterm"></a></td><td>One row per connection (regular and replication), showing information about

  122.        SSL used on this connection.

  123.        See <a class="xref" href="monitoring-stats.html#PG-STAT-SSL-VIEW" title="Table 27.8. pg_stat_ssl View">pg_stat_ssl</a> for details.

  124.       </td></tr><tr><td><code class="structname">pg_stat_gssapi</code><a id="id-1.6.14.7.6.7.2.2.6.1.2" class="indexterm"></a></td><td>One row per connection (regular and replication), showing information about

  125.        GSSAPI authentication and encryption used on this connection.

  126.        See <a class="xref" href="monitoring-stats.html#PG-STAT-GSSAPI-VIEW" title="Table 27.9. pg_stat_gssapi View">pg_stat_gssapi</a> for details.

  127.       </td></tr><tr><td><code class="structname">pg_stat_progress_create_index</code><a id="id-1.6.14.7.6.7.2.2.7.1.2" class="indexterm"></a></td><td>One row for each backend running <code class="command">CREATE INDEX</code> or <code class="command">REINDEX</code>, showing

  128.       current progress.

  129.       See <a class="xref" href="progress-reporting.html#CREATE-INDEX-PROGRESS-REPORTING" title="27.4.1. CREATE INDEX Progress Reporting">Section 27.4.1</a>.

  130.      </td></tr><tr><td><code class="structname">pg_stat_progress_vacuum</code><a id="id-1.6.14.7.6.7.2.2.8.1.2" class="indexterm"></a></td><td>One row for each backend (including autovacuum worker processes) running

  131.        <code class="command">VACUUM</code>, showing current progress.

  132.        See <a class="xref" href="progress-reporting.html#VACUUM-PROGRESS-REPORTING" title="27.4.2. VACUUM Progress Reporting">Section 27.4.2</a>.

  133.       </td></tr><tr><td><code class="structname">pg_stat_progress_cluster</code><a id="id-1.6.14.7.6.7.2.2.9.1.2" class="indexterm"></a></td><td>One row for each backend running

  134.        <code class="command">CLUSTER</code> or <code class="command">VACUUM FULL</code>, showing current progress.

  135.        See <a class="xref" href="progress-reporting.html#CLUSTER-PROGRESS-REPORTING" title="27.4.3. CLUSTER Progress Reporting">Section 27.4.3</a>.

  136.       </td></tr></tbody></table></div></div><br class="table-break" /><div class="table" id="MONITORING-STATS-VIEWS-TABLE"><p class="title"><strong>Table 27.2. Collected Statistics Views</strong></p><div class="table-contents"><table class="table" summary="Collected Statistics Views" border="1"><colgroup><col /><col /></colgroup><thead><tr><th>View Name</th><th>Description</th></tr></thead><tbody><tr><td><code class="structname">pg_stat_archiver</code><a id="id-1.6.14.7.6.8.2.2.1.1.2" class="indexterm"></a></td><td>One row only, showing statistics about the

  137.        WAL archiver process's activity. See

  138.        <a class="xref" href="monitoring-stats.html#PG-STAT-ARCHIVER-VIEW" title="Table 27.10. pg_stat_archiver View">pg_stat_archiver</a> for details.

  139.       </td></tr><tr><td><code class="structname">pg_stat_bgwriter</code><a id="id-1.6.14.7.6.8.2.2.2.1.2" class="indexterm"></a></td><td>One row only, showing statistics about the

  140.        background writer process's activity. See

  141.        <a class="xref" href="monitoring-stats.html#PG-STAT-BGWRITER-VIEW" title="Table 27.11. pg_stat_bgwriter View">pg_stat_bgwriter</a> for details.

  142.      </td></tr><tr><td><code class="structname">pg_stat_database</code><a id="id-1.6.14.7.6.8.2.2.3.1.2" class="indexterm"></a></td><td>One row per database, showing database-wide statistics. See

  143.        <a class="xref" href="monitoring-stats.html#PG-STAT-DATABASE-VIEW" title="Table 27.12. pg_stat_database View">pg_stat_database</a> for details.

  144.       </td></tr><tr><td><code class="structname">pg_stat_database_conflicts</code><a id="id-1.6.14.7.6.8.2.2.4.1.2" class="indexterm"></a></td><td>

  145.        One row per database, showing database-wide statistics about

  146.        query cancels due to conflict with recovery on standby servers.

  147.        See <a class="xref" href="monitoring-stats.html#PG-STAT-DATABASE-CONFLICTS-VIEW" title="Table 27.13. pg_stat_database_conflicts View">pg_stat_database_conflicts</a> for details.

  148.       </td></tr><tr><td><code class="structname">pg_stat_all_tables</code><a id="id-1.6.14.7.6.8.2.2.5.1.2" class="indexterm"></a></td><td>

  149.        One row for each table in the current database, showing statistics

  150.        about accesses to that specific table.

  151.        See <a class="xref" href="monitoring-stats.html#PG-STAT-ALL-TABLES-VIEW" title="Table 27.14. pg_stat_all_tables View">pg_stat_all_tables</a> for details.

  152.       </td></tr><tr><td><code class="structname">pg_stat_sys_tables</code><a id="id-1.6.14.7.6.8.2.2.6.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_stat_all_tables</code>, except that only

  153.       system tables are shown.</td></tr><tr><td><code class="structname">pg_stat_user_tables</code><a id="id-1.6.14.7.6.8.2.2.7.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_stat_all_tables</code>, except that only user

  154.       tables are shown.</td></tr><tr><td><code class="structname">pg_stat_xact_all_tables</code><a id="id-1.6.14.7.6.8.2.2.8.1.2" class="indexterm"></a></td><td>Similar to <code class="structname">pg_stat_all_tables</code>, but counts actions

  155.       taken so far within the current transaction (which are <span class="emphasis"><em>not</em></span>

  156.       yet included in <code class="structname">pg_stat_all_tables</code> and related views).

  157.       The columns for numbers of live and dead rows and vacuum and

  158.       analyze actions are not present in this view.</td></tr><tr><td><code class="structname">pg_stat_xact_sys_tables</code><a id="id-1.6.14.7.6.8.2.2.9.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_stat_xact_all_tables</code>, except that only

  159.       system tables are shown.</td></tr><tr><td><code class="structname">pg_stat_xact_user_tables</code><a id="id-1.6.14.7.6.8.2.2.10.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_stat_xact_all_tables</code>, except that only

  160.       user tables are shown.</td></tr><tr><td><code class="structname">pg_stat_all_indexes</code><a id="id-1.6.14.7.6.8.2.2.11.1.2" class="indexterm"></a></td><td>

  161.        One row for each index in the current database, showing statistics

  162.        about accesses to that specific index.

  163.        See <a class="xref" href="monitoring-stats.html#PG-STAT-ALL-INDEXES-VIEW" title="Table 27.15. pg_stat_all_indexes View">pg_stat_all_indexes</a> for details.

  164.       </td></tr><tr><td><code class="structname">pg_stat_sys_indexes</code><a id="id-1.6.14.7.6.8.2.2.12.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_stat_all_indexes</code>, except that only

  165.       indexes on system tables are shown.</td></tr><tr><td><code class="structname">pg_stat_user_indexes</code><a id="id-1.6.14.7.6.8.2.2.13.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_stat_all_indexes</code>, except that only

  166.       indexes on user tables are shown.</td></tr><tr><td><code class="structname">pg_statio_all_tables</code><a id="id-1.6.14.7.6.8.2.2.14.1.2" class="indexterm"></a></td><td>

  167.        One row for each table in the current database, showing statistics

  168.        about I/O on that specific table.

  169.        See <a class="xref" href="monitoring-stats.html#PG-STATIO-ALL-TABLES-VIEW" title="Table 27.16. pg_statio_all_tables View">pg_statio_all_tables</a> for details.

  170.       </td></tr><tr><td><code class="structname">pg_statio_sys_tables</code><a id="id-1.6.14.7.6.8.2.2.15.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_statio_all_tables</code>, except that only

  171.       system tables are shown.</td></tr><tr><td><code class="structname">pg_statio_user_tables</code><a id="id-1.6.14.7.6.8.2.2.16.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_statio_all_tables</code>, except that only

  172.       user tables are shown.</td></tr><tr><td><code class="structname">pg_statio_all_indexes</code><a id="id-1.6.14.7.6.8.2.2.17.1.2" class="indexterm"></a></td><td>

  173.        One row for each index in the current database,

  174.        showing statistics about I/O on that specific index.

  175.        See <a class="xref" href="monitoring-stats.html#PG-STATIO-ALL-INDEXES-VIEW" title="Table 27.17. pg_statio_all_indexes View">pg_statio_all_indexes</a> for details.

  176.       </td></tr><tr><td><code class="structname">pg_statio_sys_indexes</code><a id="id-1.6.14.7.6.8.2.2.18.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_statio_all_indexes</code>, except that only

  177.       indexes on system tables are shown.</td></tr><tr><td><code class="structname">pg_statio_user_indexes</code><a id="id-1.6.14.7.6.8.2.2.19.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_statio_all_indexes</code>, except that only

  178.       indexes on user tables are shown.</td></tr><tr><td><code class="structname">pg_statio_all_sequences</code><a id="id-1.6.14.7.6.8.2.2.20.1.2" class="indexterm"></a></td><td>

  179.        One row for each sequence in the current database,

  180.        showing statistics about I/O on that specific sequence.

  181.        See <a class="xref" href="monitoring-stats.html#PG-STATIO-ALL-SEQUENCES-VIEW" title="Table 27.18. pg_statio_all_sequences View">pg_statio_all_sequences</a> for details.

  182.      </td></tr><tr><td><code class="structname">pg_statio_sys_sequences</code><a id="id-1.6.14.7.6.8.2.2.21.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_statio_all_sequences</code>, except that only

  183.       system sequences are shown.  (Presently, no system sequences are defined,

  184.       so this view is always empty.)</td></tr><tr><td><code class="structname">pg_statio_user_sequences</code><a id="id-1.6.14.7.6.8.2.2.22.1.2" class="indexterm"></a></td><td>Same as <code class="structname">pg_statio_all_sequences</code>, except that only

  185.       user sequences are shown.</td></tr><tr><td><code class="structname">pg_stat_user_functions</code><a id="id-1.6.14.7.6.8.2.2.23.1.2" class="indexterm"></a></td><td>

  186.        One row for each tracked function, showing statistics

  187.        about executions of that function. See

  188.        <a class="xref" href="monitoring-stats.html#PG-STAT-USER-FUNCTIONS-VIEW" title="Table 27.19. pg_stat_user_functions View">pg_stat_user_functions</a> for details.

  189.       </td></tr><tr><td><code class="structname">pg_stat_xact_user_functions</code><a id="id-1.6.14.7.6.8.2.2.24.1.2" class="indexterm"></a></td><td>Similar to <code class="structname">pg_stat_user_functions</code>, but counts only

  190.       calls during the current transaction (which are <span class="emphasis"><em>not</em></span>

  191.       yet included in <code class="structname">pg_stat_user_functions</code>).</td></tr></tbody></table></div></div><br class="table-break" /><p>

  192.    The per-index statistics are particularly useful to determine which

  193.    indexes are being used and how effective they are.

  194.   </p><p>

  195.    The <code class="structname">pg_statio_</code> views are primarily useful to

  196.    determine the effectiveness of the buffer cache.  When the number

  197.    of actual disk reads is much smaller than the number of buffer

  198.    hits, then the cache is satisfying most read requests without

  199.    invoking a kernel call. However, these statistics do not give the

  200.    entire story: due to the way in which <span class="productname">PostgreSQL</span>

  201.    handles disk I/O, data that is not in the

  202.    <span class="productname">PostgreSQL</span> buffer cache might still reside in the

  203.    kernel's I/O cache, and might therefore still be fetched without

  204.    requiring a physical read. Users interested in obtaining more

  205.    detailed information on <span class="productname">PostgreSQL</span> I/O behavior are

  206.    advised to use the <span class="productname">PostgreSQL</span> statistics collector

  207.    in combination with operating system utilities that allow insight

  208.    into the kernel's handling of I/O.

  209.   </p><div class="table" id="PG-STAT-ACTIVITY-VIEW"><p class="title"><strong>Table 27.3. <code class="structname">pg_stat_activity</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_activity View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">datid</code></td><td><code class="type">oid</code></td><td>OID of the database this backend is connected to</td></tr><tr><td><code class="structfield">datname</code></td><td><code class="type">name</code></td><td>Name of the database this backend is connected to</td></tr><tr><td><code class="structfield">pid</code></td><td><code class="type">integer</code></td><td>Process ID of this backend</td></tr><tr><td><code class="structfield">usesysid</code></td><td><code class="type">oid</code></td><td>OID of the user logged into this backend</td></tr><tr><td><code class="structfield">usename</code></td><td><code class="type">name</code></td><td>Name of the user logged into this backend</td></tr><tr><td><code class="structfield">application_name</code></td><td><code class="type">text</code></td><td>Name of the application that is connected

  210.       to this backend</td></tr><tr><td><code class="structfield">client_addr</code></td><td><code class="type">inet</code></td><td>IP address of the client connected to this backend.

  211.       If this field is null, it indicates either that the client is

  212.       connected via a Unix socket on the server machine or that this is an

  213.       internal process such as autovacuum.

  214.      </td></tr><tr><td><code class="structfield">client_hostname</code></td><td><code class="type">text</code></td><td>Host name of the connected client, as reported by a

  215.       reverse DNS lookup of <code class="structfield">client_addr</code>. This field will

  216.       only be non-null for IP connections, and only when <a class="xref" href="runtime-config-logging.html#GUC-LOG-HOSTNAME">log_hostname</a> is enabled.

  217.      </td></tr><tr><td><code class="structfield">client_port</code></td><td><code class="type">integer</code></td><td>TCP port number that the client is using for communication

  218.       with this backend, or <code class="literal">-1</code> if a Unix socket is used

  219.      </td></tr><tr><td><code class="structfield">backend_start</code></td><td><code class="type">timestamp with time zone</code></td><td>Time when this process was started.  For client backends,

  220.       this is the time the client connected to the server.

  221.      </td></tr><tr><td><code class="structfield">xact_start</code></td><td><code class="type">timestamp with time zone</code></td><td>Time when this process' current transaction was started, or null

  222.       if no transaction is active. If the current

  223.       query is the first of its transaction, this column is equal to the

  224.       <code class="structfield">query_start</code> column.

  225.      </td></tr><tr><td><code class="structfield">query_start</code></td><td><code class="type">timestamp with time zone</code></td><td>Time when the currently active query was started, or if

  226.       <code class="structfield">state</code> is not <code class="literal">active</code>, when the last query

  227.       was started

  228.      </td></tr><tr><td><code class="structfield">state_change</code></td><td><code class="type">timestamp with time zone</code></td><td>Time when the <code class="structfield">state</code> was last changed</td></tr><tr><td><code class="structfield">wait_event_type</code></td><td><code class="type">text</code></td><td>The type of event for which the backend is waiting, if any;

  229.        otherwise NULL. Possible values are:

  230.        <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  231.           <code class="literal">LWLock</code>: The backend is waiting for a lightweight lock.

  232.           Each such lock protects a particular data structure in shared memory.

  233.           <code class="literal">wait_event</code> will contain a name identifying the purpose

  234.           of the lightweight lock.  (Some locks have specific names; others

  235.           are part of a group of locks each with a similar purpose.)

  236.          </p></li><li class="listitem"><p>

  237.           <code class="literal">Lock</code>: The backend is waiting for a heavyweight lock.

  238.           Heavyweight locks, also known as lock manager locks or simply locks,

  239.           primarily protect SQL-visible objects such as tables.  However,

  240.           they are also used to ensure mutual exclusion for certain internal

  241.           operations such as relation extension.  <code class="literal">wait_event</code> will

  242.           identify the type of lock awaited.

  243.          </p></li><li class="listitem"><p>

  244.           <code class="literal">BufferPin</code>: The server process is waiting to access to

  245.           a data buffer during a period when no other process can be

  246.           examining that buffer.  Buffer pin waits can be protracted if

  247.           another process holds an open cursor which last read data from the

  248.           buffer in question.

  249.          </p></li><li class="listitem"><p>

  250.           <code class="literal">Activity</code>: The server process is idle.  This is used by

  251.           system processes waiting for activity in their main processing loop.

  252.           <code class="literal">wait_event</code> will identify the specific wait point.

  253.          </p></li><li class="listitem"><p>

  254.           <code class="literal">Extension</code>: The server process is waiting for activity

  255.           in an extension module.  This category is useful for modules to

  256.           track custom waiting points.

  257.          </p></li><li class="listitem"><p>

  258.           <code class="literal">Client</code>: The server process is waiting for some activity

  259.           on a socket from user applications, and that the server expects

  260.           something to happen that is independent from its internal processes.

  261.           <code class="literal">wait_event</code> will identify the specific wait point.

  262.          </p></li><li class="listitem"><p>

  263.           <code class="literal">IPC</code>: The server process is waiting for some activity

  264.           from another process in the server.  <code class="literal">wait_event</code> will

  265.           identify the specific wait point.

  266.          </p></li><li class="listitem"><p>

  267.           <code class="literal">Timeout</code>: The server process is waiting for a timeout

  268.           to expire.  <code class="literal">wait_event</code> will identify the specific wait

  269.           point.

  270.          </p></li><li class="listitem"><p>

  271.           <code class="literal">IO</code>: The server process is waiting for a IO to complete.

  272.           <code class="literal">wait_event</code> will identify the specific wait point.

  273.          </p></li></ul></div>

  274.       </td></tr><tr><td><code class="structfield">wait_event</code></td><td><code class="type">text</code></td><td>Wait event name if backend is currently waiting, otherwise NULL.

  275.      See <a class="xref" href="monitoring-stats.html#WAIT-EVENT-TABLE" title="Table 27.4. wait_event Description">Table 27.4</a> for details.

  276.      </td></tr><tr><td><code class="structfield">state</code></td><td><code class="type">text</code></td><td>Current overall state of this backend.

  277.        Possible values are:

  278.        <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  279.            <code class="literal">active</code>: The backend is executing a query.

  280.           </p></li><li class="listitem"><p>

  281.            <code class="literal">idle</code>: The backend is waiting for a new client command.

  282.           </p></li><li class="listitem"><p>

  283.            <code class="literal">idle in transaction</code>: The backend is in a transaction,

  284.            but is not currently executing a query.

  285.           </p></li><li class="listitem"><p>

  286.            <code class="literal">idle in transaction (aborted)</code>: This state is similar to

  287.            <code class="literal">idle in transaction</code>, except one of the statements in

  288.            the transaction caused an error.

  289.           </p></li><li class="listitem"><p>

  290.            <code class="literal">fastpath function call</code>: The backend is executing a

  291.            fast-path function.

  292.           </p></li><li class="listitem"><p>

  293.            <code class="literal">disabled</code>: This state is reported if <a class="xref" href="runtime-config-statistics.html#GUC-TRACK-ACTIVITIES">track_activities</a> is disabled in this backend.

  294.           </p></li></ul></div>

  295.      </td></tr><tr><td><code class="structfield">backend_xid</code></td><td><code class="type">xid</code></td><td>Top-level transaction identifier of this backend, if any.</td></tr><tr><td><code class="structfield">backend_xmin</code></td><td><code class="type">xid</code></td><td>The current backend's <code class="literal">xmin</code> horizon.</td></tr><tr><td><code class="structfield">query</code></td><td><code class="type">text</code></td><td>Text of this backend's most recent query. If

  296.       <code class="structfield">state</code> is <code class="literal">active</code> this field shows the

  297.       currently executing query. In all other states, it shows the last query

  298.       that was executed. By default the query text is truncated at 1024

  299.       bytes; this value can be changed via the parameter

  300.       <a class="xref" href="runtime-config-statistics.html#GUC-TRACK-ACTIVITY-QUERY-SIZE">track_activity_query_size</a>.

  301.      </td></tr><tr><td><code class="structfield">backend_type</code></td><td><code class="type">text</code></td><td>Type of current backend. Possible types are

  302.       <code class="literal">autovacuum launcher</code>, <code class="literal">autovacuum worker</code>,

  303.       <code class="literal">logical replication launcher</code>,

  304.       <code class="literal">logical replication worker</code>,

  305.       <code class="literal">parallel worker</code>, <code class="literal">background writer</code>,

  306.       <code class="literal">client backend</code>, <code class="literal">checkpointer</code>,

  307.       <code class="literal">startup</code>, <code class="literal">walreceiver</code>,

  308.       <code class="literal">walsender</code> and <code class="literal">walwriter</code>.

  309.       In addition, background workers registered by extensions may have

  310.       additional types.

  311.      </td></tr></tbody></table></div></div><br class="table-break" /><p>

  312.    The <code class="structname">pg_stat_activity</code> view will have one row

  313.    per server process, showing information related to

  314.    the current activity of that process.

  315.   </p><div class="note"><h3 class="title">Note</h3><p>

  316.     The <code class="structfield">wait_event</code> and <code class="structfield">state</code> columns are

  317.     independent.  If a backend is in the <code class="literal">active</code> state,

  318.     it may or may not be <code class="literal">waiting</code> on some event.  If the state

  319.     is <code class="literal">active</code> and <code class="structfield">wait_event</code> is non-null, it

  320.     means that a query is being executed, but is being blocked somewhere

  321.     in the system.

  322.    </p></div><div class="table" id="WAIT-EVENT-TABLE"><p class="title"><strong>Table 27.4. <code class="structname">wait_event</code> Description</strong></p><div class="table-contents"><table class="table" summary="wait_event Description" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Wait Event Type</th><th>Wait Event Name</th><th>Description</th></tr></thead><tbody><tr><td rowspan="65"><code class="literal">LWLock</code></td><td><code class="literal">ShmemIndexLock</code></td><td>Waiting to find or allocate space in shared memory.</td></tr><tr><td><code class="literal">OidGenLock</code></td><td>Waiting to allocate or assign an OID.</td></tr><tr><td><code class="literal">XidGenLock</code></td><td>Waiting to allocate or assign a transaction id.</td></tr><tr><td><code class="literal">ProcArrayLock</code></td><td>Waiting to get a snapshot or clearing a transaction id at

  323.          transaction end.</td></tr><tr><td><code class="literal">SInvalReadLock</code></td><td>Waiting to retrieve or remove messages from shared invalidation

  324.          queue.</td></tr><tr><td><code class="literal">SInvalWriteLock</code></td><td>Waiting to add a message in shared invalidation queue.</td></tr><tr><td><code class="literal">WALBufMappingLock</code></td><td>Waiting to replace a page in WAL buffers.</td></tr><tr><td><code class="literal">WALWriteLock</code></td><td>Waiting for WAL buffers to be written to disk.</td></tr><tr><td><code class="literal">ControlFileLock</code></td><td>Waiting to read or update the control file or creation of a

  325.          new WAL file.</td></tr><tr><td><code class="literal">CheckpointLock</code></td><td>Waiting to perform checkpoint.</td></tr><tr><td><code class="literal">CLogControlLock</code></td><td>Waiting to read or update transaction status.</td></tr><tr><td><code class="literal">SubtransControlLock</code></td><td>Waiting to read or update sub-transaction information.</td></tr><tr><td><code class="literal">MultiXactGenLock</code></td><td>Waiting to read or update shared multixact state.</td></tr><tr><td><code class="literal">MultiXactOffsetControlLock</code></td><td>Waiting to read or update multixact offset mappings.</td></tr><tr><td><code class="literal">MultiXactMemberControlLock</code></td><td>Waiting to read or update multixact member mappings.</td></tr><tr><td><code class="literal">RelCacheInitLock</code></td><td>Waiting to read or write relation cache initialization

  326.          file.</td></tr><tr><td><code class="literal">CheckpointerCommLock</code></td><td>Waiting to manage fsync requests.</td></tr><tr><td><code class="literal">TwoPhaseStateLock</code></td><td>Waiting to read or update the state of prepared transactions.</td></tr><tr><td><code class="literal">TablespaceCreateLock</code></td><td>Waiting to create or drop the tablespace.</td></tr><tr><td><code class="literal">BtreeVacuumLock</code></td><td>Waiting to read or update vacuum-related information for a

  327.           B-tree index.</td></tr><tr><td><code class="literal">AddinShmemInitLock</code></td><td>Waiting to manage space allocation in shared memory.</td></tr><tr><td><code class="literal">AutovacuumLock</code></td><td>Autovacuum worker or launcher waiting to update or

  328.          read the current state of autovacuum workers.</td></tr><tr><td><code class="literal">AutovacuumScheduleLock</code></td><td>Waiting to ensure that the table it has selected for a vacuum

  329.          still needs vacuuming.

  330.          </td></tr><tr><td><code class="literal">SyncScanLock</code></td><td>Waiting to get the start location of a scan on a table for

  331.          synchronized scans.</td></tr><tr><td><code class="literal">RelationMappingLock</code></td><td>Waiting to update the relation map file used to store catalog

  332.          to filenode mapping.

  333.          </td></tr><tr><td><code class="literal">AsyncCtlLock</code></td><td>Waiting to read or update shared notification state.</td></tr><tr><td><code class="literal">AsyncQueueLock</code></td><td>Waiting to read or update notification messages.</td></tr><tr><td><code class="literal">SerializableXactHashLock</code></td><td>Waiting to retrieve or store information about serializable

  334.          transactions.</td></tr><tr><td><code class="literal">SerializableFinishedListLock</code></td><td>Waiting to access the list of finished serializable

  335.          transactions.</td></tr><tr><td><code class="literal">SerializablePredicateLockListLock</code></td><td>Waiting to perform an operation on a list of locks held by

  336.          serializable transactions.</td></tr><tr><td><code class="literal">OldSerXidLock</code></td><td>Waiting to read or record conflicting serializable

  337.          transactions.</td></tr><tr><td><code class="literal">SyncRepLock</code></td><td>Waiting to read or update information about synchronous

  338.          replicas.</td></tr><tr><td><code class="literal">BackgroundWorkerLock</code></td><td>Waiting to read or update background worker state.</td></tr><tr><td><code class="literal">DynamicSharedMemoryControlLock</code></td><td>Waiting to read or update dynamic shared memory state.</td></tr><tr><td><code class="literal">AutoFileLock</code></td><td>Waiting to update the <code class="filename">postgresql.auto.conf</code> file.</td></tr><tr><td><code class="literal">ReplicationSlotAllocationLock</code></td><td>Waiting to allocate or free a replication slot.</td></tr><tr><td><code class="literal">ReplicationSlotControlLock</code></td><td>Waiting to read or update replication slot state.</td></tr><tr><td><code class="literal">CommitTsControlLock</code></td><td>Waiting to read or update transaction commit timestamps.</td></tr><tr><td><code class="literal">CommitTsLock</code></td><td>Waiting to read or update the last value set for the

  339.          transaction timestamp.</td></tr><tr><td><code class="literal">ReplicationOriginLock</code></td><td>Waiting to setup, drop or use replication origin.</td></tr><tr><td><code class="literal">MultiXactTruncationLock</code></td><td>Waiting to read or truncate multixact information.</td></tr><tr><td><code class="literal">OldSnapshotTimeMapLock</code></td><td>Waiting to read or update old snapshot control information.</td></tr><tr><td><code class="literal">LogicalRepWorkerLock</code></td><td>Waiting for action on logical replication worker to finish.</td></tr><tr><td><code class="literal">CLogTruncationLock</code></td><td>Waiting to execute <code class="function">txid_status</code> or update

  340.          the oldest transaction id available to it.</td></tr><tr><td><code class="literal">clog</code></td><td>Waiting for I/O on a clog (transaction status) buffer.</td></tr><tr><td><code class="literal">commit_timestamp</code></td><td>Waiting for I/O on commit timestamp buffer.</td></tr><tr><td><code class="literal">subtrans</code></td><td>Waiting for I/O a subtransaction buffer.</td></tr><tr><td><code class="literal">multixact_offset</code></td><td>Waiting for I/O on a multixact offset buffer.</td></tr><tr><td><code class="literal">multixact_member</code></td><td>Waiting for I/O on a multixact_member buffer.</td></tr><tr><td><code class="literal">async</code></td><td>Waiting for I/O on an async (notify) buffer.</td></tr><tr><td><code class="literal">oldserxid</code></td><td>Waiting for I/O on an oldserxid buffer.</td></tr><tr><td><code class="literal">wal_insert</code></td><td>Waiting to insert WAL into a memory buffer.</td></tr><tr><td><code class="literal">buffer_content</code></td><td>Waiting to read or write a data page in memory.</td></tr><tr><td><code class="literal">buffer_io</code></td><td>Waiting for I/O on a data page.</td></tr><tr><td><code class="literal">replication_origin</code></td><td>Waiting to read or update the replication progress.</td></tr><tr><td><code class="literal">replication_slot_io</code></td><td>Waiting for I/O on a replication slot.</td></tr><tr><td><code class="literal">proc</code></td><td>Waiting to read or update the fast-path lock information.</td></tr><tr><td><code class="literal">buffer_mapping</code></td><td>Waiting to associate a data block with a buffer in the buffer

  341.          pool.</td></tr><tr><td><code class="literal">lock_manager</code></td><td>Waiting to add or examine locks for backends, or waiting to

  342.          join or exit a locking group (used by parallel query).</td></tr><tr><td><code class="literal">predicate_lock_manager</code></td><td>Waiting to add or examine predicate lock information.</td></tr><tr><td><code class="literal">serializable_xact</code></td><td>Waiting to perform an operation on a serializable transaction

  343.          in a parallel query.</td></tr><tr><td><code class="literal">parallel_query_dsa</code></td><td>Waiting for parallel query dynamic shared memory allocation lock.</td></tr><tr><td><code class="literal">tbm</code></td><td>Waiting for TBM shared iterator lock.</td></tr><tr><td><code class="literal">parallel_append</code></td><td>Waiting to choose the next subplan during Parallel Append plan

  344.          execution.</td></tr><tr><td><code class="literal">parallel_hash_join</code></td><td>Waiting to allocate or exchange a chunk of memory or update

  345.          counters during Parallel Hash plan execution.</td></tr><tr><td rowspan="10"><code class="literal">Lock</code></td><td><code class="literal">relation</code></td><td>Waiting to acquire a lock on a relation.</td></tr><tr><td><code class="literal">extend</code></td><td>Waiting to extend a relation.</td></tr><tr><td><code class="literal">page</code></td><td>Waiting to acquire a lock on page of a relation.</td></tr><tr><td><code class="literal">tuple</code></td><td>Waiting to acquire a lock on a tuple.</td></tr><tr><td><code class="literal">transactionid</code></td><td>Waiting for a transaction to finish.</td></tr><tr><td><code class="literal">virtualxid</code></td><td>Waiting to acquire a virtual xid lock.</td></tr><tr><td><code class="literal">speculative token</code></td><td>Waiting to acquire a speculative insertion lock.</td></tr><tr><td><code class="literal">object</code></td><td>Waiting to acquire a lock on a non-relation database object.</td></tr><tr><td><code class="literal">userlock</code></td><td>Waiting to acquire a user lock.</td></tr><tr><td><code class="literal">advisory</code></td><td>Waiting to acquire an advisory user lock.</td></tr><tr><td><code class="literal">BufferPin</code></td><td><code class="literal">BufferPin</code></td><td>Waiting to acquire a pin on a buffer.</td></tr><tr><td rowspan="14"><code class="literal">Activity</code></td><td><code class="literal">ArchiverMain</code></td><td>Waiting in main loop of the archiver process.</td></tr><tr><td><code class="literal">AutoVacuumMain</code></td><td>Waiting in main loop of autovacuum launcher process.</td></tr><tr><td><code class="literal">BgWriterHibernate</code></td><td>Waiting in background writer process, hibernating.</td></tr><tr><td><code class="literal">BgWriterMain</code></td><td>Waiting in main loop of background writer process background worker.</td></tr><tr><td><code class="literal">CheckpointerMain</code></td><td>Waiting in main loop of checkpointer process.</td></tr><tr><td><code class="literal">LogicalApplyMain</code></td><td>Waiting in main loop of logical apply process.</td></tr><tr><td><code class="literal">LogicalLauncherMain</code></td><td>Waiting in main loop of logical launcher process.</td></tr><tr><td><code class="literal">PgStatMain</code></td><td>Waiting in main loop of the statistics collector process.</td></tr><tr><td><code class="literal">RecoveryWalAll</code></td><td>Waiting for WAL from a stream at recovery.</td></tr><tr><td><code class="literal">RecoveryWalStream</code></td><td>

  346.           Waiting when WAL data is not available from any kind of sources

  347.           (local, archive or stream) before trying again to retrieve WAL data,

  348.           at recovery.

  349.          </td></tr><tr><td><code class="literal">SysLoggerMain</code></td><td>Waiting in main loop of syslogger process.</td></tr><tr><td><code class="literal">WalReceiverMain</code></td><td>Waiting in main loop of WAL receiver process.</td></tr><tr><td><code class="literal">WalSenderMain</code></td><td>Waiting in main loop of WAL sender process.</td></tr><tr><td><code class="literal">WalWriterMain</code></td><td>Waiting in main loop of WAL writer process.</td></tr><tr><td rowspan="9"><code class="literal">Client</code></td><td><code class="literal">ClientRead</code></td><td>Waiting to read data from the client.</td></tr><tr><td><code class="literal">ClientWrite</code></td><td>Waiting to write data to the client.</td></tr><tr><td><code class="literal">GSSOpenServer</code></td><td>Waiting to read data from the client while establishing the GSSAPI session.</td></tr><tr><td><code class="literal">LibPQWalReceiverConnect</code></td><td>Waiting in WAL receiver to establish connection to remote server.</td></tr><tr><td><code class="literal">LibPQWalReceiverReceive</code></td><td>Waiting in WAL receiver to receive data from remote server.</td></tr><tr><td><code class="literal">SSLOpenServer</code></td><td>Waiting for SSL while attempting connection.</td></tr><tr><td><code class="literal">WalReceiverWaitStart</code></td><td>Waiting for startup process to send initial data for streaming replication.</td></tr><tr><td><code class="literal">WalSenderWaitForWAL</code></td><td>Waiting for WAL to be flushed in WAL sender process.</td></tr><tr><td><code class="literal">WalSenderWriteData</code></td><td>Waiting for any activity when processing replies from WAL receiver in WAL sender process.</td></tr><tr><td><code class="literal">Extension</code></td><td><code class="literal">Extension</code></td><td>Waiting in an extension.</td></tr><tr><td rowspan="37"><code class="literal">IPC</code></td><td><code class="literal">BgWorkerShutdown</code></td><td>Waiting for background worker to shut down.</td></tr><tr><td><code class="literal">BgWorkerStartup</code></td><td>Waiting for background worker to start up.</td></tr><tr><td><code class="literal">BtreePage</code></td><td>Waiting for the page number needed to continue a parallel B-tree scan to become available.</td></tr><tr><td><code class="literal">CheckpointDone</code></td><td>Waiting for a checkpoint to complete.</td></tr><tr><td><code class="literal">CheckpointStart</code></td><td>Waiting for a checkpoint to start.</td></tr><tr><td><code class="literal">ClogGroupUpdate</code></td><td>Waiting for group leader to update transaction status at transaction end.</td></tr><tr><td><code class="literal">ExecuteGather</code></td><td>Waiting for activity from child process when executing <code class="literal">Gather</code> node.</td></tr><tr><td><code class="literal">Hash/Batch/Allocating</code></td><td>Waiting for an elected Parallel Hash participant to allocate a hash table.</td></tr><tr><td><code class="literal">Hash/Batch/Electing</code></td><td>Electing a Parallel Hash participant to allocate a hash table.</td></tr><tr><td><code class="literal">Hash/Batch/Loading</code></td><td>Waiting for other Parallel Hash participants to finish loading a hash table.</td></tr><tr><td><code class="literal">Hash/Build/Allocating</code></td><td>Waiting for an elected Parallel Hash participant to allocate the initial hash table.</td></tr><tr><td><code class="literal">Hash/Build/Electing</code></td><td>Electing a Parallel Hash participant to allocate the initial hash table.</td></tr><tr><td><code class="literal">Hash/Build/HashingInner</code></td><td>Waiting for other Parallel Hash participants to finish hashing the inner relation.</td></tr><tr><td><code class="literal">Hash/Build/HashingOuter</code></td><td>Waiting for other Parallel Hash participants to finish partitioning the outer relation.</td></tr><tr><td><code class="literal">Hash/GrowBatches/Allocating</code></td><td>Waiting for an elected Parallel Hash participant to allocate more batches.</td></tr><tr><td><code class="literal">Hash/GrowBatches/Deciding</code></td><td>Electing a Parallel Hash participant to decide on future batch growth.</td></tr><tr><td><code class="literal">Hash/GrowBatches/Electing</code></td><td>Electing a Parallel Hash participant to allocate more batches.</td></tr><tr><td><code class="literal">Hash/GrowBatches/Finishing</code></td><td>Waiting for an elected Parallel Hash participant to decide on future batch growth.</td></tr><tr><td><code class="literal">Hash/GrowBatches/Repartitioning</code></td><td>Waiting for other Parallel Hash participants to finishing repartitioning.</td></tr><tr><td><code class="literal">Hash/GrowBuckets/Allocating</code></td><td>Waiting for an elected Parallel Hash participant to finish allocating more buckets.</td></tr><tr><td><code class="literal">Hash/GrowBuckets/Electing</code></td><td>Electing a Parallel Hash participant to allocate more buckets.</td></tr><tr><td><code class="literal">Hash/GrowBuckets/Reinserting</code></td><td>Waiting for other Parallel Hash participants to finish inserting tuples into new buckets.</td></tr><tr><td><code class="literal">LogicalSyncData</code></td><td>Waiting for logical replication remote server to send data for initial table synchronization.</td></tr><tr><td><code class="literal">LogicalSyncStateChange</code></td><td>Waiting for logical replication remote server to change state.</td></tr><tr><td><code class="literal">MessageQueueInternal</code></td><td>Waiting for other process to be attached in shared message queue.</td></tr><tr><td><code class="literal">MessageQueuePutMessage</code></td><td>Waiting to write a protocol message to a shared message queue.</td></tr><tr><td><code class="literal">MessageQueueReceive</code></td><td>Waiting to receive bytes from a shared message queue.</td></tr><tr><td><code class="literal">MessageQueueSend</code></td><td>Waiting to send bytes to a shared message queue.</td></tr><tr><td><code class="literal">ParallelBitmapScan</code></td><td>Waiting for parallel bitmap scan to become initialized.</td></tr><tr><td><code class="literal">ParallelCreateIndexScan</code></td><td>Waiting for parallel <code class="command">CREATE INDEX</code> workers to finish heap scan.</td></tr><tr><td><code class="literal">ParallelFinish</code></td><td>Waiting for parallel workers to finish computing.</td></tr><tr><td><code class="literal">ProcArrayGroupUpdate</code></td><td>Waiting for group leader to clear transaction id at transaction end.</td></tr><tr><td><code class="literal">Promote</code></td><td>Waiting for standby promotion.</td></tr><tr><td><code class="literal">ReplicationOriginDrop</code></td><td>Waiting for a replication origin to become inactive to be dropped.</td></tr><tr><td><code class="literal">ReplicationSlotDrop</code></td><td>Waiting for a replication slot to become inactive to be dropped.</td></tr><tr><td><code class="literal">SafeSnapshot</code></td><td>Waiting for a snapshot for a <code class="literal">READ ONLY DEFERRABLE</code> transaction.</td></tr><tr><td><code class="literal">SyncRep</code></td><td>Waiting for confirmation from remote server during synchronous replication.</td></tr><tr><td rowspan="3"><code class="literal">Timeout</code></td><td><code class="literal">BaseBackupThrottle</code></td><td>Waiting during base backup when throttling activity.</td></tr><tr><td><code class="literal">PgSleep</code></td><td>Waiting in process that called <code class="function">pg_sleep</code>.</td></tr><tr><td><code class="literal">RecoveryApplyDelay</code></td><td>Waiting to apply WAL at recovery because it is delayed.</td></tr><tr><td rowspan="68"><code class="literal">IO</code></td><td><code class="literal">BufFileRead</code></td><td>Waiting for a read from a buffered file.</td></tr><tr><td><code class="literal">BufFileWrite</code></td><td>Waiting for a write to a buffered file.</td></tr><tr><td><code class="literal">ControlFileRead</code></td><td>Waiting for a read from the control file.</td></tr><tr><td><code class="literal">ControlFileSync</code></td><td>Waiting for the control file to reach stable storage.</td></tr><tr><td><code class="literal">ControlFileSyncUpdate</code></td><td>Waiting for an update to the control file to reach stable storage.</td></tr><tr><td><code class="literal">ControlFileWrite</code></td><td>Waiting for a write to the control file.</td></tr><tr><td><code class="literal">ControlFileWriteUpdate</code></td><td>Waiting for a write to update the control file.</td></tr><tr><td><code class="literal">CopyFileRead</code></td><td>Waiting for a read during a file copy operation.</td></tr><tr><td><code class="literal">CopyFileWrite</code></td><td>Waiting for a write during a file copy operation.</td></tr><tr><td><code class="literal">DataFileExtend</code></td><td>Waiting for a relation data file to be extended.</td></tr><tr><td><code class="literal">DataFileFlush</code></td><td>Waiting for a relation data file to reach stable storage.</td></tr><tr><td><code class="literal">DataFileImmediateSync</code></td><td>Waiting for an immediate synchronization of a relation data file to stable storage.</td></tr><tr><td><code class="literal">DataFilePrefetch</code></td><td>Waiting for an asynchronous prefetch from a relation data file.</td></tr><tr><td><code class="literal">DataFileRead</code></td><td>Waiting for a read from a relation data file.</td></tr><tr><td><code class="literal">DataFileSync</code></td><td>Waiting for changes to a relation data file to reach stable storage.</td></tr><tr><td><code class="literal">DataFileTruncate</code></td><td>Waiting for a relation data file to be truncated.</td></tr><tr><td><code class="literal">DataFileWrite</code></td><td>Waiting for a write to a relation data file.</td></tr><tr><td><code class="literal">DSMFillZeroWrite</code></td><td>Waiting to write zero bytes to a dynamic shared memory backing file.</td></tr><tr><td><code class="literal">LockFileAddToDataDirRead</code></td><td>Waiting for a read while adding a line to the data directory lock file.</td></tr><tr><td><code class="literal">LockFileAddToDataDirSync</code></td><td>Waiting for data to reach stable storage while adding a line to the data directory lock file.</td></tr><tr><td><code class="literal">LockFileAddToDataDirWrite</code></td><td>Waiting for a write while adding a line to the data directory lock file.</td></tr><tr><td><code class="literal">LockFileCreateRead</code></td><td>Waiting to read while creating the data directory lock file.</td></tr><tr><td><code class="literal">LockFileCreateSync</code></td><td>Waiting for data to reach stable storage while creating the data directory lock file.</td></tr><tr><td><code class="literal">LockFileCreateWrite</code></td><td>Waiting for a write while creating the data directory lock file.</td></tr><tr><td><code class="literal">LockFileReCheckDataDirRead</code></td><td>Waiting for a read during recheck of the data directory lock file.</td></tr><tr><td><code class="literal">LogicalRewriteCheckpointSync</code></td><td>Waiting for logical rewrite mappings to reach stable storage during a checkpoint.</td></tr><tr><td><code class="literal">LogicalRewriteMappingSync</code></td><td>Waiting for mapping data to reach stable storage during a logical rewrite.</td></tr><tr><td><code class="literal">LogicalRewriteMappingWrite</code></td><td>Waiting for a write of mapping data during a logical rewrite.</td></tr><tr><td><code class="literal">LogicalRewriteSync</code></td><td>Waiting for logical rewrite mappings to reach stable storage.</td></tr><tr><td><code class="literal">LogicalRewriteTruncate</code></td><td>Waiting for truncate of mapping data during a logical rewrite.</td></tr><tr><td><code class="literal">LogicalRewriteWrite</code></td><td>Waiting for a write of logical rewrite mappings.</td></tr><tr><td><code class="literal">RelationMapRead</code></td><td>Waiting for a read of the relation map file.</td></tr><tr><td><code class="literal">RelationMapSync</code></td><td>Waiting for the relation map file to reach stable storage.</td></tr><tr><td><code class="literal">RelationMapWrite</code></td><td>Waiting for a write to the relation map file.</td></tr><tr><td><code class="literal">ReorderBufferRead</code></td><td>Waiting for a read during reorder buffer management.</td></tr><tr><td><code class="literal">ReorderBufferWrite</code></td><td>Waiting for a write during reorder buffer management.</td></tr><tr><td><code class="literal">ReorderLogicalMappingRead</code></td><td>Waiting for a read of a logical mapping during reorder buffer management.</td></tr><tr><td><code class="literal">ReplicationSlotRead</code></td><td>Waiting for a read from a replication slot control file.</td></tr><tr><td><code class="literal">ReplicationSlotRestoreSync</code></td><td>Waiting for a replication slot control file to reach stable storage while restoring it to memory.</td></tr><tr><td><code class="literal">ReplicationSlotSync</code></td><td>Waiting for a replication slot control file to reach stable storage.</td></tr><tr><td><code class="literal">ReplicationSlotWrite</code></td><td>Waiting for a write to a replication slot control file.</td></tr><tr><td><code class="literal">SLRUFlushSync</code></td><td>Waiting for SLRU data to reach stable storage during a checkpoint or database shutdown.</td></tr><tr><td><code class="literal">SLRURead</code></td><td>Waiting for a read of an SLRU page.</td></tr><tr><td><code class="literal">SLRUSync</code></td><td>Waiting for SLRU data to reach stable storage following a page write.</td></tr><tr><td><code class="literal">SLRUWrite</code></td><td>Waiting for a write of an SLRU page.</td></tr><tr><td><code class="literal">SnapbuildRead</code></td><td>Waiting for a read of a serialized historical catalog snapshot.</td></tr><tr><td><code class="literal">SnapbuildSync</code></td><td>Waiting for a serialized historical catalog snapshot to reach stable storage.</td></tr><tr><td><code class="literal">SnapbuildWrite</code></td><td>Waiting for a write of a serialized historical catalog snapshot.</td></tr><tr><td><code class="literal">TimelineHistoryFileSync</code></td><td>Waiting for a timeline history file received via streaming replication to reach stable storage.</td></tr><tr><td><code class="literal">TimelineHistoryFileWrite</code></td><td>Waiting for a write of a timeline history file received via streaming replication.</td></tr><tr><td><code class="literal">TimelineHistoryRead</code></td><td>Waiting for a read of a timeline history file.</td></tr><tr><td><code class="literal">TimelineHistorySync</code></td><td>Waiting for a newly created timeline history file to reach stable storage.</td></tr><tr><td><code class="literal">TimelineHistoryWrite</code></td><td>Waiting for a write of a newly created timeline history file.</td></tr><tr><td><code class="literal">TwophaseFileRead</code></td><td>Waiting for a read of a two phase state file.</td></tr><tr><td><code class="literal">TwophaseFileSync</code></td><td>Waiting for a two phase state file to reach stable storage.</td></tr><tr><td><code class="literal">TwophaseFileWrite</code></td><td>Waiting for a write of a two phase state file.</td></tr><tr><td><code class="literal">WALBootstrapSync</code></td><td>Waiting for WAL to reach stable storage during bootstrapping.</td></tr><tr><td><code class="literal">WALBootstrapWrite</code></td><td>Waiting for a write of a WAL page during bootstrapping.</td></tr><tr><td><code class="literal">WALCopyRead</code></td><td>Waiting for a read when creating a new WAL segment by copying an existing one.</td></tr><tr><td><code class="literal">WALCopySync</code></td><td>Waiting a new WAL segment created by copying an existing one to reach stable storage.</td></tr><tr><td><code class="literal">WALCopyWrite</code></td><td>Waiting for a write when creating a new WAL segment by copying an existing one.</td></tr><tr><td><code class="literal">WALInitSync</code></td><td>Waiting for a newly initialized WAL file to reach stable storage.</td></tr><tr><td><code class="literal">WALInitWrite</code></td><td>Waiting for a write while initializing a new WAL file.</td></tr><tr><td><code class="literal">WALRead</code></td><td>Waiting for a read from a WAL file.</td></tr><tr><td><code class="literal">WALSenderTimelineHistoryRead</code></td><td>Waiting for a read from a timeline history file during walsender timeline command.</td></tr><tr><td><code class="literal">WALSync</code></td><td>Waiting for a WAL file to reach stable storage.</td></tr><tr><td><code class="literal">WALSyncMethodAssign</code></td><td>Waiting for data to reach stable storage while assigning WAL sync method.</td></tr><tr><td><code class="literal">WALWrite</code></td><td>Waiting for a write to a WAL file.</td></tr></tbody></table></div></div><br class="table-break" /><div class="note"><h3 class="title">Note</h3><p>

  350.      For tranches registered by extensions, the name is specified by extension

  351.      and this will be displayed as <code class="structfield">wait_event</code>.  It is quite

  352.      possible that user has registered the tranche in one of the backends (by

  353.      having allocation in dynamic shared memory) in which case other backends

  354.      won't have that information, so we display <code class="literal">extension</code> for such

  355.      cases.

  356.     </p></div><p>

  357.      Here is an example of how wait events can be viewed

  358. 

  359. </p><pre class="programlisting">

  360. SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event is NOT NULL;

  361.  pid  | wait_event_type |  wait_event

  362. ------+-----------------+---------------

  363.  2540 | Lock            | relation

  364.  6644 | LWLock          | ProcArrayLock

  365. (2 rows)

  366. </pre><p>

  367.    </p><div class="table" id="PG-STAT-REPLICATION-VIEW"><p class="title"><strong>Table 27.5. <code class="structname">pg_stat_replication</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_replication View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">pid</code></td><td><code class="type">integer</code></td><td>Process ID of a WAL sender process</td></tr><tr><td><code class="structfield">usesysid</code></td><td><code class="type">oid</code></td><td>OID of the user logged into this WAL sender process</td></tr><tr><td><code class="structfield">usename</code></td><td><code class="type">name</code></td><td>Name of the user logged into this WAL sender process</td></tr><tr><td><code class="structfield">application_name</code></td><td><code class="type">text</code></td><td>Name of the application that is connected

  368.       to this WAL sender</td></tr><tr><td><code class="structfield">client_addr</code></td><td><code class="type">inet</code></td><td>IP address of the client connected to this WAL sender.

  369.       If this field is null, it indicates that the client is

  370.       connected via a Unix socket on the server machine.

  371.      </td></tr><tr><td><code class="structfield">client_hostname</code></td><td><code class="type">text</code></td><td>Host name of the connected client, as reported by a

  372.       reverse DNS lookup of <code class="structfield">client_addr</code>. This field will

  373.       only be non-null for IP connections, and only when <a class="xref" href="runtime-config-logging.html#GUC-LOG-HOSTNAME">log_hostname</a> is enabled.

  374.      </td></tr><tr><td><code class="structfield">client_port</code></td><td><code class="type">integer</code></td><td>TCP port number that the client is using for communication

  375.       with this WAL sender, or <code class="literal">-1</code> if a Unix socket is used

  376.      </td></tr><tr><td><code class="structfield">backend_start</code></td><td><code class="type">timestamp with time zone</code></td><td>Time when this process was started, i.e., when the

  377.       client connected to this WAL sender

  378.      </td></tr><tr><td><code class="structfield">backend_xmin</code></td><td><code class="type">xid</code></td><td>This standby's <code class="literal">xmin</code> horizon reported

  379.      by <a class="xref" href="runtime-config-replication.html#GUC-HOT-STANDBY-FEEDBACK">hot_standby_feedback</a>.</td></tr><tr><td><code class="structfield">state</code></td><td><code class="type">text</code></td><td>Current WAL sender state.

  380.        Possible values are:

  381.        <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  382.            <code class="literal">startup</code>: This WAL sender is starting up.

  383.           </p></li><li class="listitem"><p>

  384.            <code class="literal">catchup</code>: This WAL sender's connected standby is

  385.            catching up with the primary.

  386.           </p></li><li class="listitem"><p>

  387.            <code class="literal">streaming</code>: This WAL sender is streaming changes

  388.            after its connected standby server has caught up with the primary.

  389.           </p></li><li class="listitem"><p>

  390.            <code class="literal">backup</code>: This WAL sender is sending a backup.

  391.           </p></li><li class="listitem"><p>

  392.            <code class="literal">stopping</code>: This WAL sender is stopping.

  393.           </p></li></ul></div>

  394.      </td></tr><tr><td><code class="structfield">sent_lsn</code></td><td><code class="type">pg_lsn</code></td><td>Last write-ahead log location sent on this connection</td></tr><tr><td><code class="structfield">write_lsn</code></td><td><code class="type">pg_lsn</code></td><td>Last write-ahead log location written to disk by this standby

  395.       server</td></tr><tr><td><code class="structfield">flush_lsn</code></td><td><code class="type">pg_lsn</code></td><td>Last write-ahead log location flushed to disk by this standby

  396.       server</td></tr><tr><td><code class="structfield">replay_lsn</code></td><td><code class="type">pg_lsn</code></td><td>Last write-ahead log location replayed into the database on this

  397.       standby server</td></tr><tr><td><code class="structfield">write_lag</code></td><td><code class="type">interval</code></td><td>Time elapsed between flushing recent WAL locally and receiving

  398.       notification that this standby server has written it (but not yet

  399.       flushed it or applied it).  This can be used to gauge the delay that

  400.       <code class="literal">synchronous_commit</code> level

  401.       <code class="literal">remote_write</code> incurred while committing if this

  402.       server was configured as a synchronous standby.</td></tr><tr><td><code class="structfield">flush_lag</code></td><td><code class="type">interval</code></td><td>Time elapsed between flushing recent WAL locally and receiving

  403.       notification that this standby server has written and flushed it

  404.       (but not yet applied it).  This can be used to gauge the delay that

  405.       <code class="literal">synchronous_commit</code> level

  406.       <code class="literal">on</code> incurred while committing if this

  407.       server was configured as a synchronous standby.</td></tr><tr><td><code class="structfield">replay_lag</code></td><td><code class="type">interval</code></td><td>Time elapsed between flushing recent WAL locally and receiving

  408.       notification that this standby server has written, flushed and

  409.       applied it.  This can be used to gauge the delay that

  410.       <code class="literal">synchronous_commit</code> level

  411.       <code class="literal">remote_apply</code> incurred while committing if this

  412.       server was configured as a synchronous standby.</td></tr><tr><td><code class="structfield">sync_priority</code></td><td><code class="type">integer</code></td><td>Priority of this standby server for being chosen as the

  413.       synchronous standby in a priority-based synchronous replication.

  414.       This has no effect in a quorum-based synchronous replication.</td></tr><tr><td><code class="structfield">sync_state</code></td><td><code class="type">text</code></td><td>Synchronous state of this standby server.

  415.        Possible values are:

  416.        <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  417.            <code class="literal">async</code>: This standby server is asynchronous.

  418.           </p></li><li class="listitem"><p>

  419.            <code class="literal">potential</code>: This standby server is now asynchronous,

  420.            but can potentially become synchronous if one of current

  421.            synchronous ones fails.

  422.           </p></li><li class="listitem"><p>

  423.            <code class="literal">sync</code>: This standby server is synchronous.

  424.           </p></li><li class="listitem"><p>

  425.            <code class="literal">quorum</code>: This standby server is considered as a candidate

  426.            for quorum standbys.

  427.           </p></li></ul></div>

  428.      </td></tr><tr><td><code class="structfield">reply_time</code></td><td><code class="type">timestamp with time zone</code></td><td>Send time of last reply message received from standby server</td></tr></tbody></table></div></div><br class="table-break" /><p>

  429.    The <code class="structname">pg_stat_replication</code> view will contain one row

  430.    per WAL sender process, showing statistics about replication to that

  431.    sender's connected standby server.  Only directly connected standbys are

  432.    listed; no information is available about downstream standby servers.

  433.   </p><p>

  434.    The lag times reported in the <code class="structname">pg_stat_replication</code>

  435.    view are measurements of the time taken for recent WAL to be written,

  436.    flushed and replayed and for the sender to know about it.  These times

  437.    represent the commit delay that was (or would have been) introduced by each

  438.    synchronous commit level, if the remote server was configured as a

  439.    synchronous standby.  For an asynchronous standby, the

  440.    <code class="structfield">replay_lag</code> column approximates the delay

  441.    before recent transactions became visible to queries.  If the standby

  442.    server has entirely caught up with the sending server and there is no more

  443.    WAL activity, the most recently measured lag times will continue to be

  444.    displayed for a short time and then show NULL.

  445.   </p><p>

  446.    Lag times work automatically for physical replication. Logical decoding

  447.    plugins may optionally emit tracking messages; if they do not, the tracking

  448.    mechanism will simply display NULL lag.

  449.   </p><div class="note"><h3 class="title">Note</h3><p>

  450.     The reported lag times are not predictions of how long it will take for

  451.     the standby to catch up with the sending server assuming the current

  452.     rate of replay.  Such a system would show similar times while new WAL is

  453.     being generated, but would differ when the sender becomes idle.  In

  454.     particular, when the standby has caught up completely,

  455.     <code class="structname">pg_stat_replication</code> shows the time taken to

  456.     write, flush and replay the most recent reported WAL location rather than

  457.     zero as some users might expect.  This is consistent with the goal of

  458.     measuring synchronous commit and transaction visibility delays for

  459.     recent write transactions.

  460.     To reduce confusion for users expecting a different model of lag, the

  461.     lag columns revert to NULL after a short time on a fully replayed idle

  462.     system. Monitoring systems should choose whether to represent this

  463.     as missing data, zero or continue to display the last known value.

  464.    </p></div><div class="table" id="PG-STAT-WAL-RECEIVER-VIEW"><p class="title"><strong>Table 27.6. <code class="structname">pg_stat_wal_receiver</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_wal_receiver View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">pid</code></td><td><code class="type">integer</code></td><td>Process ID of the WAL receiver process</td></tr><tr><td><code class="structfield">status</code></td><td><code class="type">text</code></td><td>Activity status of the WAL receiver process</td></tr><tr><td><code class="structfield">receive_start_lsn</code></td><td><code class="type">pg_lsn</code></td><td>First write-ahead log location used when WAL receiver is

  465.       started</td></tr><tr><td><code class="structfield">receive_start_tli</code></td><td><code class="type">integer</code></td><td>First timeline number used when WAL receiver is started</td></tr><tr><td><code class="structfield">received_lsn</code></td><td><code class="type">pg_lsn</code></td><td>Last write-ahead log location already received and flushed to

  466.       disk, the initial value of this field being the first log location used

  467.       when WAL receiver is started</td></tr><tr><td><code class="structfield">received_tli</code></td><td><code class="type">integer</code></td><td>Timeline number of last write-ahead log location received and

  468.       flushed to disk, the initial value of this field being the timeline

  469.       number of the first log location used when WAL receiver is started

  470.      </td></tr><tr><td><code class="structfield">last_msg_send_time</code></td><td><code class="type">timestamp with time zone</code></td><td>Send time of last message received from origin WAL sender</td></tr><tr><td><code class="structfield">last_msg_receipt_time</code></td><td><code class="type">timestamp with time zone</code></td><td>Receipt time of last message received from origin WAL sender</td></tr><tr><td><code class="structfield">latest_end_lsn</code></td><td><code class="type">pg_lsn</code></td><td>Last write-ahead log location reported to origin WAL sender</td></tr><tr><td><code class="structfield">latest_end_time</code></td><td><code class="type">timestamp with time zone</code></td><td>Time of last write-ahead log location reported to origin WAL sender</td></tr><tr><td><code class="structfield">slot_name</code></td><td><code class="type">text</code></td><td>Replication slot name used by this WAL receiver</td></tr><tr><td><code class="structfield">sender_host</code></td><td><code class="type">text</code></td><td>

  471.       Host of the <span class="productname">PostgreSQL</span> instance

  472.       this WAL receiver is connected to. This can be a host name,

  473.       an IP address, or a directory path if the connection is via

  474.       Unix socket.  (The path case can be distinguished because it

  475.       will always be an absolute path, beginning with <code class="literal">/</code>.)

  476.      </td></tr><tr><td><code class="structfield">sender_port</code></td><td><code class="type">integer</code></td><td>

  477.       Port number of the <span class="productname">PostgreSQL</span> instance

  478.       this WAL receiver is connected to.

  479.      </td></tr><tr><td><code class="structfield">conninfo</code></td><td><code class="type">text</code></td><td>

  480.       Connection string used by this WAL receiver,

  481.       with security-sensitive fields obfuscated.

  482.      </td></tr></tbody></table></div></div><br class="table-break" /><p>

  483.    The <code class="structname">pg_stat_wal_receiver</code> view will contain only

  484.    one row, showing statistics about the WAL receiver from that receiver's

  485.    connected server.

  486.   </p><div class="table" id="PG-STAT-SUBSCRIPTION"><p class="title"><strong>Table 27.7. <code class="structname">pg_stat_subscription</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_subscription View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">subid</code></td><td><code class="type">oid</code></td><td>OID of the subscription</td></tr><tr><td><code class="structfield">subname</code></td><td><code class="type">text</code></td><td>Name of the subscription</td></tr><tr><td><code class="structfield">pid</code></td><td><code class="type">integer</code></td><td>Process ID of the subscription worker process</td></tr><tr><td><code class="structfield">relid</code></td><td><code class="type">Oid</code></td><td>OID of the relation that the worker is synchronizing; null for the

  487.      main apply worker</td></tr><tr><td><code class="structfield">received_lsn</code></td><td><code class="type">pg_lsn</code></td><td>Last write-ahead log location received, the initial value of

  488.       this field being 0</td></tr><tr><td><code class="structfield">last_msg_send_time</code></td><td><code class="type">timestamp with time zone</code></td><td>Send time of last message received from origin WAL sender</td></tr><tr><td><code class="structfield">last_msg_receipt_time</code></td><td><code class="type">timestamp with time zone</code></td><td>Receipt time of last message received from origin WAL sender

  489.      </td></tr><tr><td><code class="structfield">latest_end_lsn</code></td><td><code class="type">pg_lsn</code></td><td>Last write-ahead log location reported to origin WAL sender

  490.      </td></tr><tr><td><code class="structfield">latest_end_time</code></td><td><code class="type">timestamp with time zone</code></td><td>Time of last write-ahead log location reported to origin WAL

  491.       sender</td></tr></tbody></table></div></div><br class="table-break" /><p>

  492.    The <code class="structname">pg_stat_subscription</code> view will contain one

  493.    row per subscription for main worker (with null PID if the worker is

  494.    not running), and additional rows for workers handling the initial data

  495.    copy of the subscribed tables.

  496.   </p><div class="table" id="PG-STAT-SSL-VIEW"><p class="title"><strong>Table 27.8. <code class="structname">pg_stat_ssl</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_ssl View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">pid</code></td><td><code class="type">integer</code></td><td>Process ID of a backend or WAL sender process</td></tr><tr><td><code class="structfield">ssl</code></td><td><code class="type">boolean</code></td><td>True if SSL is used on this connection</td></tr><tr><td><code class="structfield">version</code></td><td><code class="type">text</code></td><td>Version of SSL in use, or NULL if SSL is not in use

  497.       on this connection</td></tr><tr><td><code class="structfield">cipher</code></td><td><code class="type">text</code></td><td>Name of SSL cipher in use, or NULL if SSL is not in use

  498.       on this connection</td></tr><tr><td><code class="structfield">bits</code></td><td><code class="type">integer</code></td><td>Number of bits in the encryption algorithm used, or NULL

  499.      if SSL is not used on this connection</td></tr><tr><td><code class="structfield">compression</code></td><td><code class="type">boolean</code></td><td>True if SSL compression is in use, false if not,

  500.       or NULL if SSL is not in use on this connection</td></tr><tr><td><code class="structfield">client_dn</code></td><td><code class="type">text</code></td><td>Distinguished Name (DN) field from the client certificate

  501.       used, or NULL if no client certificate was supplied or if SSL

  502.       is not in use on this connection. This field is truncated if the

  503.       DN field is longer than <code class="symbol">NAMEDATALEN</code> (64 characters

  504.       in a standard build).

  505.      </td></tr><tr><td><code class="structfield">client_serial</code></td><td><code class="type">numeric</code></td><td>Serial number of the client certificate, or NULL if no client

  506.      certificate was supplied or if SSL is not in use on this connection.  The

  507.      combination of certificate serial number and certificate issuer uniquely

  508.      identifies a certificate (unless the issuer erroneously reuses serial

  509.      numbers).</td></tr><tr><td><code class="structfield">issuer_dn</code></td><td><code class="type">text</code></td><td>DN of the issuer of the client certificate, or NULL if no client

  510.      certificate was supplied or if SSL is not in use on this connection.

  511.      This field is truncated like <code class="structfield">client_dn</code>.</td></tr></tbody></table></div></div><br class="table-break" /><p>

  512.    The <code class="structname">pg_stat_ssl</code> view will contain one row per

  513.    backend or WAL sender process, showing statistics about SSL usage on

  514.    this connection. It can be joined to <code class="structname">pg_stat_activity</code>

  515.    or <code class="structname">pg_stat_replication</code> on the

  516.    <code class="structfield">pid</code> column to get more details about the

  517.    connection.

  518.   </p><div class="table" id="PG-STAT-GSSAPI-VIEW"><p class="title"><strong>Table 27.9. <code class="structname">pg_stat_gssapi</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_gssapi View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">pid</code></td><td><code class="type">integer</code></td><td>Process ID of a backend</td></tr><tr><td><code class="structfield">gss_authenticated</code></td><td><code class="type">boolean</code></td><td>True if GSSAPI authentication was used for this connection</td></tr><tr><td><code class="structfield">principal</code></td><td><code class="type">text</code></td><td>Principal used to authenticate this connection, or NULL

  519.       if GSSAPI was not used to authenticate this connection.  This

  520.       field is truncated if the principal is longer than

  521.       <code class="symbol">NAMEDATALEN</code> (64 characters in a standard build).

  522.      </td></tr><tr><td><code class="structfield">encrypted</code></td><td><code class="type">boolean</code></td><td>True if GSSAPI encryption is in use on this connection</td></tr></tbody></table></div></div><br class="table-break" /><p>

  523.    The <code class="structname">pg_stat_gssapi</code> view will contain one row per

  524.    backend, showing information about GSSAPI usage on this connection. It can

  525.    be joined to <code class="structname">pg_stat_activity</code> or

  526.    <code class="structname">pg_stat_replication</code> on the

  527.    <code class="structfield">pid</code> column to get more details about the

  528.    connection.

  529.   </p><div class="table" id="PG-STAT-ARCHIVER-VIEW"><p class="title"><strong>Table 27.10. <code class="structname">pg_stat_archiver</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_archiver View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">archived_count</code></td><td><code class="type">bigint</code></td><td>Number of WAL files that have been successfully archived</td></tr><tr><td><code class="structfield">last_archived_wal</code></td><td><code class="type">text</code></td><td>Name of the last WAL file successfully archived</td></tr><tr><td><code class="structfield">last_archived_time</code></td><td><code class="type">timestamp with time zone</code></td><td>Time of the last successful archive operation</td></tr><tr><td><code class="structfield">failed_count</code></td><td><code class="type">bigint</code></td><td>Number of failed attempts for archiving WAL files</td></tr><tr><td><code class="structfield">last_failed_wal</code></td><td><code class="type">text</code></td><td>Name of the WAL file of the last failed archival operation</td></tr><tr><td><code class="structfield">last_failed_time</code></td><td><code class="type">timestamp with time zone</code></td><td>Time of the last failed archival operation</td></tr><tr><td><code class="structfield">stats_reset</code></td><td><code class="type">timestamp with time zone</code></td><td>Time at which these statistics were last reset</td></tr></tbody></table></div></div><br class="table-break" /><p>

  530.    The <code class="structname">pg_stat_archiver</code> view will always have a

  531.    single row, containing data about the archiver process of the cluster.

  532.   </p><div class="table" id="PG-STAT-BGWRITER-VIEW"><p class="title"><strong>Table 27.11. <code class="structname">pg_stat_bgwriter</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_bgwriter View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">checkpoints_timed</code></td><td><code class="type">bigint</code></td><td>Number of scheduled checkpoints that have been performed</td></tr><tr><td><code class="structfield">checkpoints_req</code></td><td><code class="type">bigint</code></td><td>Number of requested checkpoints that have been performed</td></tr><tr><td><code class="structfield">checkpoint_write_time</code></td><td><code class="type">double precision</code></td><td>

  533.         Total amount of time that has been spent in the portion of

  534.         checkpoint processing where files are written to disk, in milliseconds

  535.       </td></tr><tr><td><code class="structfield">checkpoint_sync_time</code></td><td><code class="type">double precision</code></td><td>

  536.         Total amount of time that has been spent in the portion of

  537.         checkpoint processing where files are synchronized to disk, in

  538.         milliseconds

  539.       </td></tr><tr><td><code class="structfield">buffers_checkpoint</code></td><td><code class="type">bigint</code></td><td>Number of buffers written during checkpoints</td></tr><tr><td><code class="structfield">buffers_clean</code></td><td><code class="type">bigint</code></td><td>Number of buffers written by the background writer</td></tr><tr><td><code class="structfield">maxwritten_clean</code></td><td><code class="type">bigint</code></td><td>Number of times the background writer stopped a cleaning

  540.        scan because it had written too many buffers</td></tr><tr><td><code class="structfield">buffers_backend</code></td><td><code class="type">bigint</code></td><td>Number of buffers written directly by a backend</td></tr><tr><td><code class="structfield">buffers_backend_fsync</code></td><td><code class="type">bigint</code></td><td>Number of times a backend had to execute its own

  541.        <code class="function">fsync</code> call (normally the background writer handles those

  542.        even when the backend does its own write)</td></tr><tr><td><code class="structfield">buffers_alloc</code></td><td><code class="type">bigint</code></td><td>Number of buffers allocated</td></tr><tr><td><code class="structfield">stats_reset</code></td><td><code class="type">timestamp with time zone</code></td><td>Time at which these statistics were last reset</td></tr></tbody></table></div></div><br class="table-break" /><p>

  543.    The <code class="structname">pg_stat_bgwriter</code> view will always have a

  544.    single row, containing global data for the cluster.

  545.   </p><div class="table" id="PG-STAT-DATABASE-VIEW"><p class="title"><strong>Table 27.12. <code class="structname">pg_stat_database</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_database View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">datid</code></td><td><code class="type">oid</code></td><td>OID of this database, or 0 for objects belonging to a shared

  546.      relation</td></tr><tr><td><code class="structfield">datname</code></td><td><code class="type">name</code></td><td>Name of this database, or <code class="literal">NULL</code> for the shared

  547.      objects.</td></tr><tr><td><code class="structfield">numbackends</code></td><td><code class="type">integer</code></td><td>Number of backends currently connected to this database, or

  548.      <code class="literal">NULL</code> for the shared objects.  This is the only column

  549.      in this view that returns a value reflecting current state; all other

  550.      columns return the accumulated values since the last reset.</td></tr><tr><td><code class="structfield">xact_commit</code></td><td><code class="type">bigint</code></td><td>Number of transactions in this database that have been

  551.       committed</td></tr><tr><td><code class="structfield">xact_rollback</code></td><td><code class="type">bigint</code></td><td>Number of transactions in this database that have been

  552.       rolled back</td></tr><tr><td><code class="structfield">blks_read</code></td><td><code class="type">bigint</code></td><td>Number of disk blocks read in this database</td></tr><tr><td><code class="structfield">blks_hit</code></td><td><code class="type">bigint</code></td><td>Number of times disk blocks were found already in the buffer

  553.       cache, so that a read was not necessary (this only includes hits in the

  554.       PostgreSQL buffer cache, not the operating system's file system cache)

  555.      </td></tr><tr><td><code class="structfield">tup_returned</code></td><td><code class="type">bigint</code></td><td>Number of rows returned by queries in this database</td></tr><tr><td><code class="structfield">tup_fetched</code></td><td><code class="type">bigint</code></td><td>Number of rows fetched by queries in this database</td></tr><tr><td><code class="structfield">tup_inserted</code></td><td><code class="type">bigint</code></td><td>Number of rows inserted by queries in this database</td></tr><tr><td><code class="structfield">tup_updated</code></td><td><code class="type">bigint</code></td><td>Number of rows updated by queries in this database</td></tr><tr><td><code class="structfield">tup_deleted</code></td><td><code class="type">bigint</code></td><td>Number of rows deleted by queries in this database</td></tr><tr><td><code class="structfield">conflicts</code></td><td><code class="type">bigint</code></td><td>Number of queries canceled due to conflicts with recovery

  556.       in this database. (Conflicts occur only on standby servers; see

  557.       <a class="xref" href="monitoring-stats.html#PG-STAT-DATABASE-CONFLICTS-VIEW" title="Table 27.13. pg_stat_database_conflicts View">pg_stat_database_conflicts</a> for details.)

  558.      </td></tr><tr><td><code class="structfield">temp_files</code></td><td><code class="type">bigint</code></td><td>Number of temporary files created by queries in this database.

  559.       All temporary files are counted, regardless of why the temporary file

  560.       was created (e.g., sorting or hashing), and regardless of the

  561.       <a class="xref" href="runtime-config-logging.html#GUC-LOG-TEMP-FILES">log_temp_files</a> setting.

  562.      </td></tr><tr><td><code class="structfield">temp_bytes</code></td><td><code class="type">bigint</code></td><td>Total amount of data written to temporary files by queries in

  563.       this database. All temporary files are counted, regardless of why

  564.       the temporary file was created, and

  565.       regardless of the <a class="xref" href="runtime-config-logging.html#GUC-LOG-TEMP-FILES">log_temp_files</a> setting.

  566.      </td></tr><tr><td><code class="structfield">deadlocks</code></td><td><code class="type">bigint</code></td><td>Number of deadlocks detected in this database</td></tr><tr><td><code class="structfield">checksum_failures</code></td><td><code class="type">bigint</code></td><td>Number of data page checksum failures detected in this

  567.       database (or on a shared object), or NULL if data checksums are not

  568.       enabled.</td></tr><tr><td><code class="structfield">checksum_last_failure</code></td><td><code class="type">timestamp with time zone</code></td><td>Time at which the last data page checksum failure was detected in

  569.       this database (or on a shared object), or NULL if data checksums are not

  570.       enabled.</td></tr><tr><td><code class="structfield">blk_read_time</code></td><td><code class="type">double precision</code></td><td>Time spent reading data file blocks by backends in this database,

  571.       in milliseconds</td></tr><tr><td><code class="structfield">blk_write_time</code></td><td><code class="type">double precision</code></td><td>Time spent writing data file blocks by backends in this database,

  572.       in milliseconds</td></tr><tr><td><code class="structfield">stats_reset</code></td><td><code class="type">timestamp with time zone</code></td><td>Time at which these statistics were last reset</td></tr></tbody></table></div></div><br class="table-break" /><p>

  573.    The <code class="structname">pg_stat_database</code> view will contain one row

  574.    for each database in the cluster, plus one for the shared objects, showing

  575.    database-wide statistics.

  576.   </p><div class="table" id="PG-STAT-DATABASE-CONFLICTS-VIEW"><p class="title"><strong>Table 27.13. <code class="structname">pg_stat_database_conflicts</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_database_conflicts View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">datid</code></td><td><code class="type">oid</code></td><td>OID of a database</td></tr><tr><td><code class="structfield">datname</code></td><td><code class="type">name</code></td><td>Name of this database</td></tr><tr><td><code class="structfield">confl_tablespace</code></td><td><code class="type">bigint</code></td><td>Number of queries in this database that have been canceled due to

  577.       dropped tablespaces</td></tr><tr><td><code class="structfield">confl_lock</code></td><td><code class="type">bigint</code></td><td>Number of queries in this database that have been canceled due to

  578.       lock timeouts</td></tr><tr><td><code class="structfield">confl_snapshot</code></td><td><code class="type">bigint</code></td><td>Number of queries in this database that have been canceled due to

  579.       old snapshots</td></tr><tr><td><code class="structfield">confl_bufferpin</code></td><td><code class="type">bigint</code></td><td>Number of queries in this database that have been canceled due to

  580.       pinned buffers</td></tr><tr><td><code class="structfield">confl_deadlock</code></td><td><code class="type">bigint</code></td><td>Number of queries in this database that have been canceled due to

  581.       deadlocks</td></tr></tbody></table></div></div><br class="table-break" /><p>

  582.    The <code class="structname">pg_stat_database_conflicts</code> view will contain

  583.    one row per database, showing database-wide statistics about

  584.    query cancels occurring due to conflicts with recovery on standby servers.

  585.    This view will only contain information on standby servers, since

  586.    conflicts do not occur on master servers.

  587.   </p><div class="table" id="PG-STAT-ALL-TABLES-VIEW"><p class="title"><strong>Table 27.14. <code class="structname">pg_stat_all_tables</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_all_tables View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">relid</code></td><td><code class="type">oid</code></td><td>OID of a table</td></tr><tr><td><code class="structfield">schemaname</code></td><td><code class="type">name</code></td><td>Name of the schema that this table is in</td></tr><tr><td><code class="structfield">relname</code></td><td><code class="type">name</code></td><td>Name of this table</td></tr><tr><td><code class="structfield">seq_scan</code></td><td><code class="type">bigint</code></td><td>Number of sequential scans initiated on this table</td></tr><tr><td><code class="structfield">seq_tup_read</code></td><td><code class="type">bigint</code></td><td>Number of live rows fetched by sequential scans</td></tr><tr><td><code class="structfield">idx_scan</code></td><td><code class="type">bigint</code></td><td>Number of index scans initiated on this table</td></tr><tr><td><code class="structfield">idx_tup_fetch</code></td><td><code class="type">bigint</code></td><td>Number of live rows fetched by index scans</td></tr><tr><td><code class="structfield">n_tup_ins</code></td><td><code class="type">bigint</code></td><td>Number of rows inserted</td></tr><tr><td><code class="structfield">n_tup_upd</code></td><td><code class="type">bigint</code></td><td>Number of rows updated (includes HOT updated rows)</td></tr><tr><td><code class="structfield">n_tup_del</code></td><td><code class="type">bigint</code></td><td>Number of rows deleted</td></tr><tr><td><code class="structfield">n_tup_hot_upd</code></td><td><code class="type">bigint</code></td><td>Number of rows HOT updated (i.e., with no separate index

  588.       update required)</td></tr><tr><td><code class="structfield">n_live_tup</code></td><td><code class="type">bigint</code></td><td>Estimated number of live rows</td></tr><tr><td><code class="structfield">n_dead_tup</code></td><td><code class="type">bigint</code></td><td>Estimated number of dead rows</td></tr><tr><td><code class="structfield">n_mod_since_analyze</code></td><td><code class="type">bigint</code></td><td>Estimated number of rows modified since this table was last analyzed</td></tr><tr><td><code class="structfield">last_vacuum</code></td><td><code class="type">timestamp with time zone</code></td><td>Last time at which this table was manually vacuumed

  589.       (not counting <code class="command">VACUUM FULL</code>)</td></tr><tr><td><code class="structfield">last_autovacuum</code></td><td><code class="type">timestamp with time zone</code></td><td>Last time at which this table was vacuumed by the autovacuum

  590.       daemon</td></tr><tr><td><code class="structfield">last_analyze</code></td><td><code class="type">timestamp with time zone</code></td><td>Last time at which this table was manually analyzed</td></tr><tr><td><code class="structfield">last_autoanalyze</code></td><td><code class="type">timestamp with time zone</code></td><td>Last time at which this table was analyzed by the autovacuum

  591.       daemon</td></tr><tr><td><code class="structfield">vacuum_count</code></td><td><code class="type">bigint</code></td><td>Number of times this table has been manually vacuumed

  592.       (not counting <code class="command">VACUUM FULL</code>)</td></tr><tr><td><code class="structfield">autovacuum_count</code></td><td><code class="type">bigint</code></td><td>Number of times this table has been vacuumed by the autovacuum

  593.       daemon</td></tr><tr><td><code class="structfield">analyze_count</code></td><td><code class="type">bigint</code></td><td>Number of times this table has been manually analyzed</td></tr><tr><td><code class="structfield">autoanalyze_count</code></td><td><code class="type">bigint</code></td><td>Number of times this table has been analyzed by the autovacuum

  594.       daemon</td></tr></tbody></table></div></div><br class="table-break" /><p>

  595.    The <code class="structname">pg_stat_all_tables</code> view will contain

  596.    one row for each table in the current database (including TOAST

  597.    tables), showing statistics about accesses to that specific table. The

  598.    <code class="structname">pg_stat_user_tables</code> and

  599.    <code class="structname">pg_stat_sys_tables</code> views

  600.    contain the same information,

  601.    but filtered to only show user and system tables respectively.

  602.   </p><div class="table" id="PG-STAT-ALL-INDEXES-VIEW"><p class="title"><strong>Table 27.15. <code class="structname">pg_stat_all_indexes</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_all_indexes View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">relid</code></td><td><code class="type">oid</code></td><td>OID of the table for this index</td></tr><tr><td><code class="structfield">indexrelid</code></td><td><code class="type">oid</code></td><td>OID of this index</td></tr><tr><td><code class="structfield">schemaname</code></td><td><code class="type">name</code></td><td>Name of the schema this index is in</td></tr><tr><td><code class="structfield">relname</code></td><td><code class="type">name</code></td><td>Name of the table for this index</td></tr><tr><td><code class="structfield">indexrelname</code></td><td><code class="type">name</code></td><td>Name of this index</td></tr><tr><td><code class="structfield">idx_scan</code></td><td><code class="type">bigint</code></td><td>Number of index scans initiated on this index</td></tr><tr><td><code class="structfield">idx_tup_read</code></td><td><code class="type">bigint</code></td><td>Number of index entries returned by scans on this index</td></tr><tr><td><code class="structfield">idx_tup_fetch</code></td><td><code class="type">bigint</code></td><td>Number of live table rows fetched by simple index scans using this

  603.       index</td></tr></tbody></table></div></div><br class="table-break" /><p>

  604.    The <code class="structname">pg_stat_all_indexes</code> view will contain

  605.    one row for each index in the current database,

  606.    showing statistics about accesses to that specific index. The

  607.    <code class="structname">pg_stat_user_indexes</code> and

  608.    <code class="structname">pg_stat_sys_indexes</code> views

  609.    contain the same information,

  610.    but filtered to only show user and system indexes respectively.

  611.   </p><p>

  612.    Indexes can be used by simple index scans, <span class="quote">“<span class="quote">bitmap</span>”</span> index scans,

  613.    and the optimizer.  In a bitmap scan

  614.    the output of several indexes can be combined via AND or OR rules,

  615.    so it is difficult to associate individual heap row fetches

  616.    with specific indexes when a bitmap scan is used.  Therefore, a bitmap

  617.    scan increments the

  618.    <code class="structname">pg_stat_all_indexes</code>.<code class="structfield">idx_tup_read</code>

  619.    count(s) for the index(es) it uses, and it increments the

  620.    <code class="structname">pg_stat_all_tables</code>.<code class="structfield">idx_tup_fetch</code>

  621.    count for the table, but it does not affect

  622.    <code class="structname">pg_stat_all_indexes</code>.<code class="structfield">idx_tup_fetch</code>.

  623.    The optimizer also accesses indexes to check for supplied constants

  624.    whose values are outside the recorded range of the optimizer statistics

  625.    because the optimizer statistics might be stale.

  626.   </p><div class="note"><h3 class="title">Note</h3><p>

  627.     The <code class="structfield">idx_tup_read</code> and <code class="structfield">idx_tup_fetch</code> counts

  628.     can be different even without any use of bitmap scans,

  629.     because <code class="structfield">idx_tup_read</code> counts

  630.     index entries retrieved from the index while <code class="structfield">idx_tup_fetch</code>

  631.     counts live rows fetched from the table.  The latter will be less if any

  632.     dead or not-yet-committed rows are fetched using the index, or if any

  633.     heap fetches are avoided by means of an index-only scan.

  634.    </p></div><div class="table" id="PG-STATIO-ALL-TABLES-VIEW"><p class="title"><strong>Table 27.16. <code class="structname">pg_statio_all_tables</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_statio_all_tables View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">relid</code></td><td><code class="type">oid</code></td><td>OID of a table</td></tr><tr><td><code class="structfield">schemaname</code></td><td><code class="type">name</code></td><td>Name of the schema that this table is in</td></tr><tr><td><code class="structfield">relname</code></td><td><code class="type">name</code></td><td>Name of this table</td></tr><tr><td><code class="structfield">heap_blks_read</code></td><td><code class="type">bigint</code></td><td>Number of disk blocks read from this table</td></tr><tr><td><code class="structfield">heap_blks_hit</code></td><td><code class="type">bigint</code></td><td>Number of buffer hits in this table</td></tr><tr><td><code class="structfield">idx_blks_read</code></td><td><code class="type">bigint</code></td><td>Number of disk blocks read from all indexes on this table</td></tr><tr><td><code class="structfield">idx_blks_hit</code></td><td><code class="type">bigint</code></td><td>Number of buffer hits in all indexes on this table</td></tr><tr><td><code class="structfield">toast_blks_read</code></td><td><code class="type">bigint</code></td><td>Number of disk blocks read from this table's TOAST table (if any)</td></tr><tr><td><code class="structfield">toast_blks_hit</code></td><td><code class="type">bigint</code></td><td>Number of buffer hits in this table's TOAST table (if any)</td></tr><tr><td><code class="structfield">tidx_blks_read</code></td><td><code class="type">bigint</code></td><td>Number of disk blocks read from this table's TOAST table indexes (if any)</td></tr><tr><td><code class="structfield">tidx_blks_hit</code></td><td><code class="type">bigint</code></td><td>Number of buffer hits in this table's TOAST table indexes (if any)</td></tr></tbody></table></div></div><br class="table-break" /><p>

  635.    The <code class="structname">pg_statio_all_tables</code> view will contain

  636.    one row for each table in the current database (including TOAST

  637.    tables), showing statistics about I/O on that specific table. The

  638.    <code class="structname">pg_statio_user_tables</code> and

  639.    <code class="structname">pg_statio_sys_tables</code> views

  640.    contain the same information,

  641.    but filtered to only show user and system tables respectively.

  642.   </p><div class="table" id="PG-STATIO-ALL-INDEXES-VIEW"><p class="title"><strong>Table 27.17. <code class="structname">pg_statio_all_indexes</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_statio_all_indexes View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">relid</code></td><td><code class="type">oid</code></td><td>OID of the table for this index</td></tr><tr><td><code class="structfield">indexrelid</code></td><td><code class="type">oid</code></td><td>OID of this index</td></tr><tr><td><code class="structfield">schemaname</code></td><td><code class="type">name</code></td><td>Name of the schema this index is in</td></tr><tr><td><code class="structfield">relname</code></td><td><code class="type">name</code></td><td>Name of the table for this index</td></tr><tr><td><code class="structfield">indexrelname</code></td><td><code class="type">name</code></td><td>Name of this index</td></tr><tr><td><code class="structfield">idx_blks_read</code></td><td><code class="type">bigint</code></td><td>Number of disk blocks read from this index</td></tr><tr><td><code class="structfield">idx_blks_hit</code></td><td><code class="type">bigint</code></td><td>Number of buffer hits in this index</td></tr></tbody></table></div></div><br class="table-break" /><p>

  643.    The <code class="structname">pg_statio_all_indexes</code> view will contain

  644.    one row for each index in the current database,

  645.    showing statistics about I/O on that specific index. The

  646.    <code class="structname">pg_statio_user_indexes</code> and

  647.    <code class="structname">pg_statio_sys_indexes</code> views

  648.    contain the same information,

  649.    but filtered to only show user and system indexes respectively.

  650.   </p><div class="table" id="PG-STATIO-ALL-SEQUENCES-VIEW"><p class="title"><strong>Table 27.18. <code class="structname">pg_statio_all_sequences</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_statio_all_sequences View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">relid</code></td><td><code class="type">oid</code></td><td>OID of a sequence</td></tr><tr><td><code class="structfield">schemaname</code></td><td><code class="type">name</code></td><td>Name of the schema this sequence is in</td></tr><tr><td><code class="structfield">relname</code></td><td><code class="type">name</code></td><td>Name of this sequence</td></tr><tr><td><code class="structfield">blks_read</code></td><td><code class="type">bigint</code></td><td>Number of disk blocks read from this sequence</td></tr><tr><td><code class="structfield">blks_hit</code></td><td><code class="type">bigint</code></td><td>Number of buffer hits in this sequence</td></tr></tbody></table></div></div><br class="table-break" /><p>

  651.    The <code class="structname">pg_statio_all_sequences</code> view will contain

  652.    one row for each sequence in the current database,

  653.    showing statistics about I/O on that specific sequence.

  654.   </p><div class="table" id="PG-STAT-USER-FUNCTIONS-VIEW"><p class="title"><strong>Table 27.19. <code class="structname">pg_stat_user_functions</code> View</strong></p><div class="table-contents"><table class="table" summary="pg_stat_user_functions View" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Column</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">funcid</code></td><td><code class="type">oid</code></td><td>OID of a function</td></tr><tr><td><code class="structfield">schemaname</code></td><td><code class="type">name</code></td><td>Name of the schema this function is in</td></tr><tr><td><code class="structfield">funcname</code></td><td><code class="type">name</code></td><td>Name of this function</td></tr><tr><td><code class="structfield">calls</code></td><td><code class="type">bigint</code></td><td>Number of times this function has been called</td></tr><tr><td><code class="structfield">total_time</code></td><td><code class="type">double precision</code></td><td>Total time spent in this function and all other functions

  655.      called by it, in milliseconds</td></tr><tr><td><code class="structfield">self_time</code></td><td><code class="type">double precision</code></td><td>Total time spent in this function itself, not including

  656.      other functions called by it, in milliseconds</td></tr></tbody></table></div></div><br class="table-break" /><p>

  657.    The <code class="structname">pg_stat_user_functions</code> view will contain

  658.    one row for each tracked function, showing statistics about executions of

  659.    that function.  The <a class="xref" href="runtime-config-statistics.html#GUC-TRACK-FUNCTIONS">track_functions</a> parameter

  660.    controls exactly which functions are tracked.

  661.   </p></div><div class="sect2" id="MONITORING-STATS-FUNCTIONS"><div class="titlepage"><div><div><h3 class="title">27.2.3. Statistics Functions</h3></div></div></div><p>

  662.    Other ways of looking at the statistics can be set up by writing

  663.    queries that use the same underlying statistics access functions used by

  664.    the standard views shown above.  For details such as the functions' names,

  665.    consult the definitions of the standard views.  (For example, in

  666.    <span class="application">psql</span> you could issue <code class="literal">\d+ pg_stat_activity</code>.)

  667.    The access functions for per-database statistics take a database OID as an

  668.    argument to identify which database to report on.

  669.    The per-table and per-index functions take a table or index OID.

  670.    The functions for per-function statistics take a function OID.

  671.    Note that only tables, indexes, and functions in the current database

  672.    can be seen with these functions.

  673.   </p><p>

  674.    Additional functions related to statistics collection are listed in <a class="xref" href="monitoring-stats.html#MONITORING-STATS-FUNCS-TABLE" title="Table 27.20. Additional Statistics Functions">Table 27.20</a>.

  675.   </p><div class="table" id="MONITORING-STATS-FUNCS-TABLE"><p class="title"><strong>Table 27.20. Additional Statistics Functions</strong></p><div class="table-contents"><table class="table" summary="Additional Statistics Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Function</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="literal"><code class="function">pg_backend_pid()</code></code></td><td><code class="type">integer</code></td><td>

  676.        Process ID of the server process handling the current session

  677.       </td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_activity</code>(<code class="type">integer</code>)</code><a id="id-1.6.14.7.7.4.2.2.2.1.2" class="indexterm"></a></td><td><code class="type">setof record</code></td><td>

  678.        Returns a record of information about the backend with the specified PID, or

  679.        one record for each active backend in the system if <code class="symbol">NULL</code> is

  680.        specified. The fields returned are a subset of those in the

  681.        <code class="structname">pg_stat_activity</code> view.

  682.       </td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_snapshot_timestamp()</code></code><a id="id-1.6.14.7.7.4.2.2.3.1.2" class="indexterm"></a></td><td><code class="type">timestamp with time zone</code></td><td>

  683.        Returns the timestamp of the current statistics snapshot

  684.       </td></tr><tr><td><code class="literal"><code class="function">pg_stat_clear_snapshot()</code></code><a id="id-1.6.14.7.7.4.2.2.4.1.2" class="indexterm"></a></td><td><code class="type">void</code></td><td>

  685.        Discard the current statistics snapshot

  686.       </td></tr><tr><td><code class="literal"><code class="function">pg_stat_reset()</code></code><a id="id-1.6.14.7.7.4.2.2.5.1.2" class="indexterm"></a></td><td><code class="type">void</code></td><td>

  687.        Reset all statistics counters for the current database to zero

  688.        (requires superuser privileges by default, but EXECUTE for this

  689.        function can be granted to others.)

  690.       </td></tr><tr><td><code class="literal"><code class="function">pg_stat_reset_shared</code>(text)</code><a id="id-1.6.14.7.7.4.2.2.6.1.2" class="indexterm"></a></td><td><code class="type">void</code></td><td>

  691.        Reset some cluster-wide statistics counters to zero, depending on the

  692.        argument (requires superuser privileges by default, but EXECUTE for

  693.        this function can be granted to others).

  694.        Calling <code class="literal">pg_stat_reset_shared('bgwriter')</code> will zero all the

  695.        counters shown in the <code class="structname">pg_stat_bgwriter</code> view.

  696.        Calling <code class="literal">pg_stat_reset_shared('archiver')</code> will zero all the

  697.        counters shown in the <code class="structname">pg_stat_archiver</code> view.

  698.       </td></tr><tr><td><code class="literal"><code class="function">pg_stat_reset_single_table_counters</code>(oid)</code><a id="id-1.6.14.7.7.4.2.2.7.1.2" class="indexterm"></a></td><td><code class="type">void</code></td><td>

  699.        Reset statistics for a single table or index in the current database to

  700.        zero (requires superuser privileges by default, but EXECUTE for this

  701.        function can be granted to others)

  702.       </td></tr><tr><td><code class="literal"><code class="function">pg_stat_reset_single_function_counters</code>(oid)</code><a id="id-1.6.14.7.7.4.2.2.8.1.2" class="indexterm"></a></td><td><code class="type">void</code></td><td>

  703.        Reset statistics for a single function in the current database to

  704.        zero (requires superuser privileges by default, but EXECUTE for this

  705.        function can be granted to others)

  706.       </td></tr></tbody></table></div></div><br class="table-break" /><p>

  707.    <code class="function">pg_stat_get_activity</code>, the underlying function of

  708.    the <code class="structname">pg_stat_activity</code> view, returns a set of records

  709.    containing all the available information about each backend process.

  710.    Sometimes it may be more convenient to obtain just a subset of this

  711.    information.  In such cases, an older set of per-backend statistics

  712.    access functions can be used; these are shown in <a class="xref" href="monitoring-stats.html#MONITORING-STATS-BACKEND-FUNCS-TABLE" title="Table 27.21. Per-Backend Statistics Functions">Table 27.21</a>.

  713.    These access functions use a backend ID number, which ranges from one

  714.    to the number of currently active backends.

  715.    The function <code class="function">pg_stat_get_backend_idset</code> provides a

  716.    convenient way to generate one row for each active backend for

  717.    invoking these functions.  For example, to show the <acronym class="acronym">PID</acronym>s and

  718.    current queries of all backends:

  719. 

  720. </p><pre class="programlisting">

  721. SELECT pg_stat_get_backend_pid(s.backendid) AS pid,

  722.        pg_stat_get_backend_activity(s.backendid) AS query

  723.     FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS s;

  724. </pre><p>

  725.   </p><div class="table" id="MONITORING-STATS-BACKEND-FUNCS-TABLE"><p class="title"><strong>Table 27.21. Per-Backend Statistics Functions</strong></p><div class="table-contents"><table class="table" summary="Per-Backend Statistics Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Function</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="literal"><code class="function">pg_stat_get_backend_idset()</code></code></td><td><code class="type">setof integer</code></td><td>Set of currently active backend ID numbers (from 1 to the

  726.        number of active backends)</td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_activity(integer)</code></code></td><td><code class="type">text</code></td><td>Text of this backend's most recent query</td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_activity_start(integer)</code></code></td><td><code class="type">timestamp with time zone</code></td><td>Time when the most recent query was started</td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_client_addr(integer)</code></code></td><td><code class="type">inet</code></td><td>IP address of the client connected to this backend</td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_client_port(integer)</code></code></td><td><code class="type">integer</code></td><td>TCP port number that the client is using for communication</td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_dbid(integer)</code></code></td><td><code class="type">oid</code></td><td>OID of the database this backend is connected to</td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_pid(integer)</code></code></td><td><code class="type">integer</code></td><td>Process ID of this backend</td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_start(integer)</code></code></td><td><code class="type">timestamp with time zone</code></td><td>Time when this process was started</td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_userid(integer)</code></code></td><td><code class="type">oid</code></td><td>OID of the user logged into this backend</td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_wait_event_type(integer)</code></code></td><td><code class="type">text</code></td><td>Wait event type name if backend is currently waiting, otherwise NULL.

  727.         See <a class="xref" href="monitoring-stats.html#WAIT-EVENT-TABLE" title="Table 27.4. wait_event Description">Table 27.4</a> for details.

  728.         </td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_wait_event(integer)</code></code></td><td><code class="type">text</code></td><td>Wait event name if backend is currently waiting, otherwise NULL.

  729.        See <a class="xref" href="monitoring-stats.html#WAIT-EVENT-TABLE" title="Table 27.4. wait_event Description">Table 27.4</a> for details.

  730.        </td></tr><tr><td><code class="literal"><code class="function">pg_stat_get_backend_xact_start(integer)</code></code></td><td><code class="type">timestamp with time zone</code></td><td>Time when the current transaction was started</td></tr></tbody></table></div></div><br class="table-break" /></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="monitoring-ps.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="monitoring.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="monitoring-locks.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">27.1. Standard Unix Tools </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 27.3. Viewing Locks</td></tr></table></div></body></html>
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