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Green_GoodERP18_FSJ_Standard/PostgreSQL/doc/postgresql/html/logfile-maintenance.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>24.3. Log File Maintenance</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="routine-reindex.html" title="24.2. Routine Reindexing" /><link rel="next" href="backup.html" title="Chapter 25. Backup and Restore" /></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">24.3. Log File Maintenance</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="routine-reindex.html" title="24.2. Routine Reindexing">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="maintenance.html" title="Chapter 24. Routine Database Maintenance Tasks">Up</a></td><th width="60%" align="center">Chapter 24. Routine Database Maintenance Tasks</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="backup.html" title="Chapter 25. Backup and Restore">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LOGFILE-MAINTENANCE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">24.3. Log File Maintenance</h2></div></div></div><a id="id-1.6.11.12.2" class="indexterm"></a><p>

  3.    It is a good idea to save the database server's log output

  4.    somewhere, rather than just discarding it via <code class="filename">/dev/null</code>.

  5.    The log output is invaluable when diagnosing

  6.    problems.  However, the log output tends to be voluminous

  7.    (especially at higher debug levels) so you won't want to save it

  8.    indefinitely.  You need to <span class="emphasis"><em>rotate</em></span> the log files so that

  9.    new log files are started and old ones removed after a reasonable

  10.    period of time.

  11.   </p><p>

  12.    If you simply direct the <span class="systemitem">stderr</span> of

  13.    <code class="command">postgres</code> into a

  14.    file, you will have log output, but

  15.    the only way to truncate the log file is to stop and restart

  16.    the server. This might be acceptable if you are using

  17.    <span class="productname">PostgreSQL</span> in a development environment,

  18.    but few production servers would find this behavior acceptable.

  19.   </p><p>

  20.    A better approach is to send the server's

  21.    <span class="systemitem">stderr</span> output to some type of log rotation program.

  22.    There is a built-in log rotation facility, which you can use by

  23.    setting the configuration parameter <code class="varname">logging_collector</code> to

  24.    <code class="literal">true</code> in <code class="filename">postgresql.conf</code>.  The control

  25.    parameters for this program are described in <a class="xref" href="runtime-config-logging.html#RUNTIME-CONFIG-LOGGING-WHERE" title="19.8.1. Where to Log">Section 19.8.1</a>. You can also use this approach

  26.    to capture the log data in machine readable <acronym class="acronym">CSV</acronym>

  27.    (comma-separated values) format.

  28.   </p><p>

  29.    Alternatively, you might prefer to use an external log rotation

  30.    program if you have one that you are already using with other

  31.    server software. For example, the <span class="application">rotatelogs</span>

  32.    tool included in the <span class="productname">Apache</span> distribution

  33.    can be used with <span class="productname">PostgreSQL</span>.  One way to

  34.    do this is to pipe the server's

  35.    <span class="systemitem">stderr</span> output to the desired program.

  36.    If you start the server with

  37.    <code class="command">pg_ctl</code>, then <span class="systemitem">stderr</span>

  38.    is already redirected to <span class="systemitem">stdout</span>, so you just need a

  39.    pipe command, for example:

  40. 

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

  42. pg_ctl start | rotatelogs /var/log/pgsql_log 86400

  43. </pre><p>

  44.   </p><p>

  45.    You can combine these approaches by setting up <span class="application">logrotate</span>

  46.    to collect log files produced by <span class="productname">PostgreSQL</span> built-in

  47.    logging collector.  In this case, the logging collector defines the names and

  48.    location of the log files, while <span class="application">logrotate</span>

  49.    periodically archives these files.  When initiating log rotation,

  50.    <span class="application">logrotate</span> must ensure that the application

  51.    sends further output to the new file.  This is commonly done with a

  52.    <code class="literal">postrotate</code> script that sends a <code class="literal">SIGHUP</code>

  53.    signal to the application, which then reopens the log file.

  54.    In <span class="productname">PostgreSQL</span>, you can run <code class="command">pg_ctl</code>

  55.    with the <code class="literal">logrotate</code> option instead.  When the server receives

  56.    this command, the server either switches to a new log file or reopens the

  57.    existing file, depending on the logging configuration

  58.    (see <a class="xref" href="runtime-config-logging.html#RUNTIME-CONFIG-LOGGING-WHERE" title="19.8.1. Where to Log">Section 19.8.1</a>).

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

  60.     When using static log file names, the server might fail to reopen the log

  61.     file if the max open file limit is reached or a file table overflow occurs.

  62.     In this case, log messages are sent to the old log file until a

  63.     successful log rotation. If <span class="application">logrotate</span> is

  64.     configured to compress the log file and delete it, the server may lose

  65.     the messages logged in this timeframe. To avoid this issue, you can

  66.     configure the logging collector to dynamically assign log file names

  67.     and use a <code class="literal">prerotate</code> script to ignore open log files.

  68.     </p></div><p>

  69.    Another production-grade approach to managing log output is to

  70.    send it to <span class="application">syslog</span> and let

  71.    <span class="application">syslog</span> deal with file rotation. To do this, set the

  72.    configuration parameter <code class="varname">log_destination</code> to <code class="literal">syslog</code>

  73.    (to log to <span class="application">syslog</span> only) in

  74.    <code class="filename">postgresql.conf</code>. Then you can send a <code class="literal">SIGHUP</code>

  75.    signal to the <span class="application">syslog</span> daemon whenever you want to force it

  76.    to start writing a new log file.  If you want to automate log

  77.    rotation, the <span class="application">logrotate</span> program can be

  78.    configured to work with log files from

  79.    <span class="application">syslog</span>.

  80.   </p><p>

  81.    On many systems, however, <span class="application">syslog</span> is not very reliable,

  82.    particularly with large log messages; it might truncate or drop messages

  83.    just when you need them the most.  Also, on <span class="productname">Linux</span>,

  84.    <span class="application">syslog</span> will flush each message to disk, yielding poor

  85.    performance.  (You can use a <span class="quote">“<span class="quote"><code class="literal">-</code></span>”</span> at the start of the file name

  86.    in the <span class="application">syslog</span> configuration file to disable syncing.)

  87.   </p><p>

  88.    Note that all the solutions described above take care of starting new

  89.    log files at configurable intervals, but they do not handle deletion

  90.    of old, no-longer-useful log files.  You will probably want to set

  91.    up a batch job to periodically delete old log files.  Another possibility

  92.    is to configure the rotation program so that old log files are overwritten

  93.    cyclically.

  94.   </p><p>

  95.    <a class="ulink" href="https://pgbadger.darold.net/" target="_top"><span class="productname">pgBadger</span></a>

  96.    is an external project that does sophisticated log file analysis.

  97.    <a class="ulink" href="https://bucardo.org/check_postgres/" target="_top"><span class="productname">check_postgres</span></a>

  98.    provides Nagios alerts when important messages appear in the log

  99.    files, as well as detection of many other extraordinary conditions.

  100.   </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="routine-reindex.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="maintenance.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="backup.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">24.2. Routine Reindexing </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 25. Backup and Restore</td></tr></table></div></body></html>
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