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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>52.4. Streaming Replication Protocol</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="sasl-authentication.html" title="52.3. SASL Authentication" /><link rel="next" href="protocol-logical-replication.html" title="52.5. Logical Streaming Replication Protocol" /></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">52.4. Streaming Replication Protocol</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sasl-authentication.html" title="52.3. SASL Authentication">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="protocol.html" title="Chapter 52. Frontend/Backend Protocol">Up</a></td><th width="60%" align="center">Chapter 52. Frontend/Backend Protocol</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="protocol-logical-replication.html" title="52.5. Logical Streaming Replication Protocol">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PROTOCOL-REPLICATION"><div class="titlepage"><div><div><h2 class="title" style="clear: both">52.4. Streaming Replication Protocol</h2></div></div></div><p>

  3. To initiate streaming replication, the frontend sends the

  4. <code class="literal">replication</code> parameter in the startup message. A Boolean

  5. value of <code class="literal">true</code> (or <code class="literal">on</code>,

  6. <code class="literal">yes</code>, <code class="literal">1</code>) tells the backend to go into

  7. physical replication walsender mode, wherein a small set of replication

  8. commands, shown below, can be issued instead of SQL statements.

  9. </p><p>

  10. Passing <code class="literal">database</code> as the value for the

  11. <code class="literal">replication</code> parameter instructs the backend to go into

  12. logical replication walsender mode, connecting to the database specified in

  13. the <code class="literal">dbname</code> parameter.  In logical replication walsender

  14. mode, the replication commands shown below as well as normal SQL commands can

  15. be issued.

  16. </p><p>

  17. In either physical replication or logical replication walsender mode, only the

  18. simple query protocol can be used.

  19. </p><p>

  20.  For the purpose of testing replication commands, you can make a replication

  21.  connection via <span class="application">psql</span> or any other <code class="literal">libpq</code>-using

  22.  tool with a connection string including the <code class="literal">replication</code> option,

  23.  e.g.:

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

  25. psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"

  26. </pre><p>

  27.  However, it is often more useful to use

  28.  <a class="xref" href="app-pgreceivewal.html" title="pg_receivewal"><span class="refentrytitle">pg_receivewal</span></a> (for physical replication) or

  29.  <a class="xref" href="app-pgrecvlogical.html" title="pg_recvlogical"><span class="refentrytitle"><span class="application">pg_recvlogical</span></span></a> (for logical replication).

  30. </p><p>

  31. Replication commands are logged in the server log when

  32. <a class="xref" href="runtime-config-logging.html#GUC-LOG-REPLICATION-COMMANDS">log_replication_commands</a> is enabled.

  33. </p><p>

  34. The commands accepted in replication mode are:

  35. </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">IDENTIFY_SYSTEM</code>

  36.      <a id="id-1.10.5.9.7.1.1.1.2" class="indexterm"></a>

  37.     </span></dt><dd><p>

  38.       Requests the server to identify itself. Server replies with a result

  39.       set of a single row, containing four fields:

  40.      </p><p>

  41.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  42.        <code class="literal">systemid</code> (<code class="type">text</code>)

  43.       </span></dt><dd><p>

  44.        The unique system identifier identifying the cluster. This

  45.        can be used to check that the base backup used to initialize the

  46.        standby came from the same cluster.

  47.       </p></dd><dt><span class="term">

  48.        <code class="literal">timeline</code> (<code class="type">int4</code>)

  49.       </span></dt><dd><p>

  50.        Current timeline ID. Also useful to check that the standby is

  51.        consistent with the master.

  52.       </p></dd><dt><span class="term">

  53.        <code class="literal">xlogpos</code> (<code class="type">text</code>)

  54.       </span></dt><dd><p>

  55.        Current WAL flush location. Useful to get a known location in the

  56.        write-ahead log where streaming can start.

  57.       </p></dd><dt><span class="term">

  58.        <code class="literal">dbname</code> (<code class="type">text</code>)

  59.       </span></dt><dd><p>

  60.        Database connected to or null.

  61.       </p></dd></dl></div><p>

  62.      </p></dd><dt><span class="term"><code class="literal">SHOW</code> <em class="replaceable"><code>name</code></em>

  63.      <a id="id-1.10.5.9.7.1.2.1.3" class="indexterm"></a>

  64.     </span></dt><dd><p>

  65.       Requests the server to send the current setting of a run-time parameter.

  66.       This is similar to the SQL command <a class="xref" href="sql-show.html" title="SHOW"><span class="refentrytitle">SHOW</span></a>.

  67.      </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>name</code></em></span></dt><dd><p>

  68.           The name of a run-time parameter. Available parameters are documented

  69.           in <a class="xref" href="runtime-config.html" title="Chapter 19. Server Configuration">Chapter 19</a>.

  70.          </p></dd></dl></div></dd><dt><span class="term"><code class="literal">TIMELINE_HISTORY</code> <em class="replaceable"><code>tli</code></em>

  71.      <a id="id-1.10.5.9.7.1.3.1.3" class="indexterm"></a>

  72.     </span></dt><dd><p>

  73.       Requests the server to send over the timeline history file for timeline

  74.       <em class="replaceable"><code>tli</code></em>.  Server replies with a

  75.       result set of a single row, containing two fields:

  76.      </p><p>

  77.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  78.        <code class="literal">filename</code> (<code class="type">text</code>)

  79.       </span></dt><dd><p>

  80.        File name of the timeline history file, e.g., <code class="filename">00000002.history</code>.

  81.       </p></dd><dt><span class="term">

  82.        <code class="literal">content</code> (<code class="type">bytea</code>)

  83.       </span></dt><dd><p>

  84.        Contents of the timeline history file.

  85.       </p></dd></dl></div><p>

  86.      </p></dd><dt id="PROTOCOL-REPLICATION-CREATE-SLOT"><span class="term"><code class="literal">CREATE_REPLICATION_SLOT</code> <em class="replaceable"><code>slot_name</code></em> [ <code class="literal">TEMPORARY</code> ] { <code class="literal">PHYSICAL</code> [ <code class="literal">RESERVE_WAL</code> ] | <code class="literal">LOGICAL</code> <em class="replaceable"><code>output_plugin</code></em> [ <code class="literal">EXPORT_SNAPSHOT</code> | <code class="literal">NOEXPORT_SNAPSHOT</code> | <code class="literal">USE_SNAPSHOT</code> ] }

  87.      <a id="id-1.10.5.9.7.1.4.1.11" class="indexterm"></a>

  88.     </span></dt><dd><p>

  89.       Create a physical or logical replication

  90.       slot. See <a class="xref" href="warm-standby.html#STREAMING-REPLICATION-SLOTS" title="26.2.6. Replication Slots">Section 26.2.6</a> for more about

  91.       replication slots.

  92.      </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>slot_name</code></em></span></dt><dd><p>

  93.           The name of the slot to create. Must be a valid replication slot

  94.           name (see <a class="xref" href="warm-standby.html#STREAMING-REPLICATION-SLOTS-MANIPULATION" title="26.2.6.1. Querying and Manipulating Replication Slots">Section 26.2.6.1</a>).

  95.          </p></dd><dt><span class="term"><em class="replaceable"><code>output_plugin</code></em></span></dt><dd><p>

  96.           The name of the output plugin used for logical decoding

  97.           (see <a class="xref" href="logicaldecoding-output-plugin.html" title="48.6. Logical Decoding Output Plugins">Section 48.6</a>).

  98.          </p></dd><dt><span class="term"><code class="literal">TEMPORARY</code></span></dt><dd><p>

  99.          Specify that this replication slot is a temporary one. Temporary

  100.          slots are not saved to disk and are automatically dropped on error

  101.          or when the session has finished.

  102.         </p></dd><dt><span class="term"><code class="literal">RESERVE_WAL</code></span></dt><dd><p>

  103.          Specify that this physical replication slot reserves <acronym class="acronym">WAL</acronym>

  104.          immediately.  Otherwise, <acronym class="acronym">WAL</acronym> is only reserved upon

  105.          connection from a streaming replication client.

  106.         </p></dd><dt><span class="term"><code class="literal">EXPORT_SNAPSHOT</code><br /></span><span class="term"><code class="literal">NOEXPORT_SNAPSHOT</code><br /></span><span class="term"><code class="literal">USE_SNAPSHOT</code></span></dt><dd><p>

  107.          Decides what to do with the snapshot created during logical slot

  108.          initialization. <code class="literal">EXPORT_SNAPSHOT</code>, which is the default,

  109.          will export the snapshot for use in other sessions. This option can't

  110.          be used inside a transaction.  <code class="literal">USE_SNAPSHOT</code> will use the

  111.          snapshot for the current transaction executing the command. This

  112.          option must be used in a transaction, and

  113.          <code class="literal">CREATE_REPLICATION_SLOT</code> must be the first command

  114.          run in that transaction.  Finally, <code class="literal">NOEXPORT_SNAPSHOT</code> will

  115.          just use the snapshot for logical decoding as normal but won't do

  116.          anything else with it.

  117.         </p></dd></dl></div><p>

  118.       In response to this command, the server will send a one-row result set

  119.       containing the following fields:

  120. 

  121.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">slot_name</code> (<code class="type">text</code>)</span></dt><dd><p>

  122.           The name of the newly-created replication slot.

  123.          </p></dd><dt><span class="term"><code class="literal">consistent_point</code> (<code class="type">text</code>)</span></dt><dd><p>

  124.           The WAL location at which the slot became consistent.  This is the

  125.           earliest location from which streaming can start on this replication

  126.           slot.

  127.          </p></dd><dt><span class="term"><code class="literal">snapshot_name</code> (<code class="type">text</code>)</span></dt><dd><p>

  128.           The identifier of the snapshot exported by the command.  The

  129.           snapshot is valid until a new command is executed on this connection

  130.           or the replication connection is closed.  Null if the created slot

  131.           is physical.

  132.          </p></dd><dt><span class="term"><code class="literal">output_plugin</code> (<code class="type">text</code>)</span></dt><dd><p>

  133.           The name of the output plugin used by the newly-created replication

  134.           slot.  Null if the created slot is physical.

  135.          </p></dd></dl></div><p>

  136.      </p></dd><dt><span class="term"><code class="literal">START_REPLICATION</code> [ <code class="literal">SLOT</code> <em class="replaceable"><code>slot_name</code></em> ] [ <code class="literal">PHYSICAL</code> ] <em class="replaceable"><code>XXX/XXX</code></em> [ <code class="literal">TIMELINE</code> <em class="replaceable"><code>tli</code></em> ]

  137.      <a id="id-1.10.5.9.7.1.5.1.8" class="indexterm"></a>

  138.     </span></dt><dd><p>

  139.       Instructs server to start streaming WAL, starting at

  140.       WAL location <em class="replaceable"><code>XXX/XXX</code></em>.

  141.       If <code class="literal">TIMELINE</code> option is specified,

  142.       streaming starts on timeline <em class="replaceable"><code>tli</code></em>;

  143.       otherwise, the server's current timeline is selected. The server can

  144.       reply with an error, for example if the requested section of WAL has already

  145.       been recycled. On success, server responds with a CopyBothResponse

  146.       message, and then starts to stream WAL to the frontend.

  147.      </p><p>

  148.       If a slot's name is provided

  149.       via <em class="replaceable"><code>slot_name</code></em>, it will be updated

  150.       as replication progresses so that the server knows which WAL segments,

  151.       and if <code class="varname">hot_standby_feedback</code> is on which transactions,

  152.       are still needed by the standby.

  153.      </p><p>

  154.       If the client requests a timeline that's not the latest but is part of

  155.       the history of the server, the server will stream all the WAL on that

  156.       timeline starting from the requested start point up to the point where

  157.       the server switched to another timeline. If the client requests

  158.       streaming at exactly the end of an old timeline, the server responds

  159.       immediately with CommandComplete without entering COPY mode.

  160.      </p><p>

  161.       After streaming all the WAL on a timeline that is not the latest one,

  162.       the server will end streaming by exiting the COPY mode. When the client

  163.       acknowledges this by also exiting COPY mode, the server sends a result

  164.       set with one row and two columns, indicating the next timeline in this

  165.       server's history. The first column is the next timeline's ID (type <code class="type">int8</code>), and the

  166.       second column is the WAL location where the switch happened (type <code class="type">text</code>). Usually,

  167.       the switch position is the end of the WAL that was streamed, but there

  168.       are corner cases where the server can send some WAL from the old

  169.       timeline that it has not itself replayed before promoting. Finally, the

  170.       server sends CommandComplete message, and is ready to accept a new

  171.       command.

  172.      </p><p>

  173.       WAL data is sent as a series of CopyData messages.  (This allows

  174.       other information to be intermixed; in particular the server can send

  175.       an ErrorResponse message if it encounters a failure after beginning

  176.       to stream.)  The payload of each CopyData message from server to the

  177.       client contains a message of one of the following formats:

  178.      </p><p>

  179.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  180.           XLogData (B)

  181.       </span></dt><dd><p>

  182.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  183.           Byte1('w')

  184.       </span></dt><dd><p>

  185.           Identifies the message as WAL data.

  186.       </p></dd><dt><span class="term">

  187.           Int64

  188.       </span></dt><dd><p>

  189.           The starting point of the WAL data in this message.

  190.       </p></dd><dt><span class="term">

  191.           Int64

  192.       </span></dt><dd><p>

  193.           The current end of WAL on the server.

  194.       </p></dd><dt><span class="term">

  195.           Int64

  196.       </span></dt><dd><p>

  197.           The server's system clock at the time of transmission, as

  198.           microseconds since midnight on 2000-01-01.

  199.       </p></dd><dt><span class="term">

  200.           Byte<em class="replaceable"><code>n</code></em>

  201.       </span></dt><dd><p>

  202.           A section of the WAL data stream.

  203.       </p><p>

  204.           A single WAL record is never split across two XLogData messages.

  205.           When a WAL record crosses a WAL page boundary, and is therefore

  206.           already split using continuation records, it can be split at the page

  207.           boundary. In other words, the first main WAL record and its

  208.           continuation records can be sent in different XLogData messages.

  209.       </p></dd></dl></div><p>

  210.       </p></dd><dt><span class="term">

  211.           Primary keepalive message (B)

  212.       </span></dt><dd><p>

  213.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  214.           Byte1('k')

  215.       </span></dt><dd><p>

  216.           Identifies the message as a sender keepalive.

  217.       </p></dd><dt><span class="term">

  218.           Int64

  219.       </span></dt><dd><p>

  220.           The current end of WAL on the server.

  221.       </p></dd><dt><span class="term">

  222.           Int64

  223.       </span></dt><dd><p>

  224.           The server's system clock at the time of transmission, as

  225.           microseconds since midnight on 2000-01-01.

  226.       </p></dd><dt><span class="term">

  227.           Byte1

  228.       </span></dt><dd><p>

  229.           1 means that the client should reply to this message as soon as

  230.           possible, to avoid a timeout disconnect. 0 otherwise.

  231.       </p></dd></dl></div><p>

  232.       </p></dd></dl></div><p>

  233.      </p><p>

  234.        The receiving process can send replies back to the sender at any time,

  235.        using one of the following message formats (also in the payload of a

  236.        CopyData message):

  237.      </p><p>

  238.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  239.           Standby status update (F)

  240.       </span></dt><dd><p>

  241.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  242.           Byte1('r')

  243.       </span></dt><dd><p>

  244.           Identifies the message as a receiver status update.

  245.       </p></dd><dt><span class="term">

  246.           Int64

  247.       </span></dt><dd><p>

  248.           The location of the last WAL byte + 1 received and written to disk

  249.           in the standby.

  250.       </p></dd><dt><span class="term">

  251.           Int64

  252.       </span></dt><dd><p>

  253.           The location of the last WAL byte + 1 flushed to disk in

  254.           the standby.

  255.       </p></dd><dt><span class="term">

  256.           Int64

  257.       </span></dt><dd><p>

  258.           The location of the last WAL byte + 1 applied in the standby.

  259.       </p></dd><dt><span class="term">

  260.           Int64

  261.       </span></dt><dd><p>

  262.           The client's system clock at the time of transmission, as

  263.           microseconds since midnight on 2000-01-01.

  264.       </p></dd><dt><span class="term">

  265.           Byte1

  266.       </span></dt><dd><p>

  267.           If 1, the client requests the server to reply to this message

  268.           immediately. This can be used to ping the server, to test if

  269.           the connection is still healthy.

  270.       </p></dd></dl></div><p>

  271.       </p></dd></dl></div><p>

  272.      </p><p>

  273.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  274.           Hot Standby feedback message (F)

  275.       </span></dt><dd><p>

  276.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  277.           Byte1('h')

  278.       </span></dt><dd><p>

  279.           Identifies the message as a Hot Standby feedback message.

  280.       </p></dd><dt><span class="term">

  281.           Int64

  282.       </span></dt><dd><p>

  283.           The client's system clock at the time of transmission, as

  284.           microseconds since midnight on 2000-01-01.

  285.       </p></dd><dt><span class="term">

  286.           Int32

  287.       </span></dt><dd><p>

  288.           The standby's current global xmin, excluding the catalog_xmin from any

  289.           replication slots. If both this value and the following

  290.           catalog_xmin are 0 this is treated as a notification that Hot Standby

  291.           feedback will no longer be sent on this connection. Later non-zero

  292.           messages may reinitiate the feedback mechanism.

  293.       </p></dd><dt><span class="term">

  294.           Int32

  295.       </span></dt><dd><p>

  296.           The epoch of the global xmin xid on the standby.

  297.       </p></dd><dt><span class="term">

  298.           Int32

  299.       </span></dt><dd><p>

  300.           The lowest catalog_xmin of any replication slots on the standby. Set to 0

  301.           if no catalog_xmin exists on the standby or if hot standby feedback is being

  302.           disabled.

  303.       </p></dd><dt><span class="term">

  304.           Int32

  305.       </span></dt><dd><p>

  306.           The epoch of the catalog_xmin xid on the standby.

  307.       </p></dd></dl></div><p>

  308.       </p></dd></dl></div><p>

  309.      </p></dd><dt><span class="term"><code class="literal">START_REPLICATION</code> <code class="literal">SLOT</code> <em class="replaceable"><code>slot_name</code></em> <code class="literal">LOGICAL</code> <em class="replaceable"><code>XXX/XXX</code></em> [ ( <em class="replaceable"><code>option_name</code></em> [ <em class="replaceable"><code>option_value</code></em> ] [, ...] ) ]</span></dt><dd><p>

  310.       Instructs server to start streaming WAL for logical replication, starting

  311.       at WAL location <em class="replaceable"><code>XXX/XXX</code></em>. The server can

  312.       reply with an error, for example if the requested section of WAL has already

  313.       been recycled. On success, server responds with a CopyBothResponse

  314.       message, and then starts to stream WAL to the frontend.

  315.      </p><p>

  316.       The messages inside the CopyBothResponse messages are of the same format

  317.       documented for <code class="literal">START_REPLICATION ... PHYSICAL</code>.

  318.      </p><p>

  319.       The output plugin associated with the selected slot is used

  320.       to process the output for streaming.

  321.      </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">SLOT</code> <em class="replaceable"><code>slot_name</code></em></span></dt><dd><p>

  322.           The name of the slot to stream changes from. This parameter is required,

  323.           and must correspond to an existing logical replication slot created

  324.           with <code class="literal">CREATE_REPLICATION_SLOT</code> in

  325.           <code class="literal">LOGICAL</code> mode.

  326.          </p></dd><dt><span class="term"><em class="replaceable"><code>XXX/XXX</code></em></span></dt><dd><p>

  327.          The WAL location to begin streaming at.

  328.         </p></dd><dt><span class="term"><em class="replaceable"><code>option_name</code></em></span></dt><dd><p>

  329.          The name of an option passed to the slot's logical decoding plugin.

  330.         </p></dd><dt><span class="term"><em class="replaceable"><code>option_value</code></em></span></dt><dd><p>

  331.          Optional value, in the form of a string constant, associated with the

  332.          specified option.

  333.         </p></dd></dl></div></dd><dt><span class="term">

  334.      <code class="literal">DROP_REPLICATION_SLOT</code> <em class="replaceable"><code>slot_name</code></em> [<span class="optional"> <code class="literal">WAIT</code> </span>]

  335.      <a id="id-1.10.5.9.7.1.7.1.4" class="indexterm"></a>

  336.     </span></dt><dd><p>

  337.       Drops a replication slot, freeing any reserved server-side resources.

  338.       If the slot is a logical slot that was created in a database other than

  339.       the database the walsender is connected to, this command fails.

  340.      </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>slot_name</code></em></span></dt><dd><p>

  341.           The name of the slot to drop.

  342.          </p></dd><dt><span class="term"><code class="literal">WAIT</code></span></dt><dd><p>

  343.          This option causes the command to wait if the slot is active until

  344.          it becomes inactive, instead of the default behavior of raising an

  345.          error.

  346.         </p></dd></dl></div></dd><dt><span class="term"><code class="literal">BASE_BACKUP</code> [ <code class="literal">LABEL</code> <em class="replaceable"><code>'label'</code></em> ] [ <code class="literal">PROGRESS</code> ] [ <code class="literal">FAST</code> ] [ <code class="literal">WAL</code> ] [ <code class="literal">NOWAIT</code> ] [ <code class="literal">MAX_RATE</code> <em class="replaceable"><code>rate</code></em> ] [ <code class="literal">TABLESPACE_MAP</code> ] [ <code class="literal">NOVERIFY_CHECKSUMS</code> ]

  347.      <a id="id-1.10.5.9.7.1.8.1.12" class="indexterm"></a>

  348.     </span></dt><dd><p>

  349.       Instructs the server to start streaming a base backup.

  350.       The system will automatically be put in backup mode before the backup

  351.       is started, and taken out of it when the backup is complete. The

  352.       following options are accepted:

  353.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">LABEL</code> <em class="replaceable"><code>'label'</code></em></span></dt><dd><p>

  354.           Sets the label of the backup. If none is specified, a backup label

  355.           of <code class="literal">base backup</code> will be used. The quoting rules

  356.           for the label are the same as a standard SQL string with

  357.           <a class="xref" href="runtime-config-compatible.html#GUC-STANDARD-CONFORMING-STRINGS">standard_conforming_strings</a> turned on.

  358.          </p></dd><dt><span class="term"><code class="literal">PROGRESS</code></span></dt><dd><p>

  359.           Request information required to generate a progress report. This will

  360.           send back an approximate size in the header of each tablespace, which

  361.           can be used to calculate how far along the stream is done. This is

  362.           calculated by enumerating all the file sizes once before the transfer

  363.           is even started, and might as such have a negative impact on the

  364.           performance.  In particular, it might take longer before the first data

  365.           is streamed. Since the database files can change during the backup,

  366.           the size is only approximate and might both grow and shrink between

  367.           the time of approximation and the sending of the actual files.

  368.          </p></dd><dt><span class="term"><code class="literal">FAST</code></span></dt><dd><p>

  369.           Request a fast checkpoint.

  370.          </p></dd><dt><span class="term"><code class="literal">WAL</code></span></dt><dd><p>

  371.           Include the necessary WAL segments in the backup. This will include

  372.           all the files between start and stop backup in the

  373.           <code class="filename">pg_wal</code> directory of the base directory tar

  374.           file.

  375.          </p></dd><dt><span class="term"><code class="literal">NOWAIT</code></span></dt><dd><p>

  376.           By default, the backup will wait until the last required WAL

  377.           segment has been archived, or emit a warning if log archiving is

  378.           not enabled. Specifying <code class="literal">NOWAIT</code> disables both

  379.           the waiting and the warning, leaving the client responsible for

  380.           ensuring the required log is available.

  381.          </p></dd><dt><span class="term"><code class="literal">MAX_RATE</code> <em class="replaceable"><code>rate</code></em></span></dt><dd><p>

  382.           Limit (throttle) the maximum amount of data transferred from server

  383.           to client per unit of time.  The expected unit is kilobytes per second.

  384.           If this option is specified, the value must either be equal to zero

  385.           or it must fall within the range from 32 kB through 1 GB (inclusive).

  386.           If zero is passed or the option is not specified, no restriction is

  387.           imposed on the transfer.

  388.          </p></dd><dt><span class="term"><code class="literal">TABLESPACE_MAP</code></span></dt><dd><p>

  389.           Include information about symbolic links present in the directory

  390.           <code class="filename">pg_tblspc</code> in a file named

  391.           <code class="filename">tablespace_map</code>. The tablespace map file includes

  392.           each symbolic link name as it exists in the directory

  393.           <code class="filename">pg_tblspc/</code> and the full path of that symbolic link.

  394.          </p></dd><dt><span class="term"><code class="literal">NOVERIFY_CHECKSUMS</code></span></dt><dd><p>

  395.           By default, checksums are verified during a base backup if they are

  396.           enabled. Specifying <code class="literal">NOVERIFY_CHECKSUMS</code> disables

  397.           this verification.

  398.          </p></dd></dl></div><p>

  399.      </p><p>

  400.       When the backup is started, the server will first send two

  401.       ordinary result sets, followed by one or more CopyResponse

  402.       results.

  403.      </p><p>

  404.       The first ordinary result set contains the starting position of the

  405.       backup, in a single row with two columns. The first column contains

  406.       the start position given in XLogRecPtr format, and the second column

  407.       contains the corresponding timeline ID.

  408.      </p><p>

  409.       The second ordinary result set has one row for each tablespace.

  410.       The fields in this row are:

  411.       </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">spcoid</code> (<code class="type">oid</code>)</span></dt><dd><p>

  412.           The OID of the tablespace, or null if it's the base

  413.           directory.

  414.          </p></dd><dt><span class="term"><code class="literal">spclocation</code> (<code class="type">text</code>)</span></dt><dd><p>

  415.           The full path of the tablespace directory, or null

  416.           if it's the base directory.

  417.          </p></dd><dt><span class="term"><code class="literal">size</code> (<code class="type">int8</code>)</span></dt><dd><p>

  418.           The approximate size of the tablespace, if progress report has

  419.           been requested; otherwise it's null.

  420.          </p></dd></dl></div><p>

  421.      </p><p>

  422.       After the second regular result set, one or more CopyResponse results

  423.       will be sent, one for the main data directory and one for each additional tablespace other

  424.       than <code class="literal">pg_default</code> and <code class="literal">pg_global</code>. The data in

  425.       the CopyResponse results will be a tar format (following the

  426.       <span class="quote">“<span class="quote">ustar interchange format</span>”</span> specified in the POSIX 1003.1-2008

  427.       standard) dump of the tablespace contents, except that the two trailing

  428.       blocks of zeroes specified in the standard are omitted.

  429.       After the tar data is complete, a final ordinary result set will be sent,

  430.       containing the WAL end position of the backup, in the same format as

  431.       the start position.

  432.      </p><p>

  433.       The tar archive for the data directory and each tablespace will contain

  434.       all files in the directories, regardless of whether they are

  435.       <span class="productname">PostgreSQL</span> files or other files added to the same

  436.       directory. The only excluded files are:

  437.       </p><div class="itemizedlist"><ul class="itemizedlist compact" style="list-style-type: bullet; "><li class="listitem" style="list-style-type: disc"><p>

  438.          <code class="filename">postmaster.pid</code>

  439.         </p></li><li class="listitem" style="list-style-type: disc"><p>

  440.          <code class="filename">postmaster.opts</code>

  441.         </p></li><li class="listitem" style="list-style-type: disc"><p>

  442.          <code class="filename">pg_internal.init</code> (found in multiple directories)

  443.         </p></li><li class="listitem" style="list-style-type: disc"><p>

  444.          Various temporary files and directories created during the operation

  445.          of the PostgreSQL server, such as any file or directory beginning

  446.          with <code class="filename">pgsql_tmp</code> and temporary relations.

  447.         </p></li><li class="listitem" style="list-style-type: disc"><p>

  448.          Unlogged relations, except for the init fork which is required to

  449.          recreate the (empty) unlogged relation on recovery.

  450.         </p></li><li class="listitem" style="list-style-type: disc"><p>

  451.          <code class="filename">pg_wal</code>, including subdirectories. If the backup is run

  452.          with WAL files included, a synthesized version of <code class="filename">pg_wal</code> will be

  453.          included, but it will only contain the files necessary for the

  454.          backup to work, not the rest of the contents.

  455.         </p></li><li class="listitem" style="list-style-type: disc"><p>

  456.          <code class="filename">pg_dynshmem</code>, <code class="filename">pg_notify</code>,

  457.          <code class="filename">pg_replslot</code>, <code class="filename">pg_serial</code>,

  458.          <code class="filename">pg_snapshots</code>, <code class="filename">pg_stat_tmp</code>, and

  459.          <code class="filename">pg_subtrans</code> are copied as empty directories (even if

  460.          they are symbolic links).

  461.         </p></li><li class="listitem" style="list-style-type: disc"><p>

  462.          Files other than regular files and directories, such as symbolic

  463.          links (other than for the directories listed above) and special

  464.          device files, are skipped.  (Symbolic links

  465.          in <code class="filename">pg_tblspc</code> are maintained.)

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

  467.       Owner, group, and file mode are set if the underlying file system on

  468.       the server supports it.

  469.      </p></dd></dl></div><p>

  470. 

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