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diff --git a/doc/src/sgml/html/runtime-config-replication.html b/doc/src/sgml/html/runtime-config-replication.html new file mode 100644 index 0000000..85c2656 --- /dev/null +++ b/doc/src/sgml/html/runtime-config-replication.html @@ -0,0 +1,562 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!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>20.6. Replication</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 Vsnapshot" /><link rel="prev" href="runtime-config-wal.html" title="20.5. Write Ahead Log" /><link rel="next" href="runtime-config-query.html" title="20.7. Query Planning" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">20.6. Replication</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="runtime-config-wal.html" title="20.5. Write Ahead Log">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="runtime-config.html" title="Chapter 20. Server Configuration">Up</a></td><th width="60%" align="center">Chapter 20. Server Configuration</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="runtime-config-query.html" title="20.7. Query Planning">Next</a></td></tr></table><hr /></div><div class="sect1" id="RUNTIME-CONFIG-REPLICATION"><div class="titlepage"><div><div><h2 class="title" style="clear: both">20.6. Replication</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="runtime-config-replication.html#RUNTIME-CONFIG-REPLICATION-SENDER">20.6.1. Sending Servers</a></span></dt><dt><span class="sect2"><a href="runtime-config-replication.html#RUNTIME-CONFIG-REPLICATION-PRIMARY">20.6.2. Primary Server</a></span></dt><dt><span class="sect2"><a href="runtime-config-replication.html#RUNTIME-CONFIG-REPLICATION-STANDBY">20.6.3. Standby Servers</a></span></dt><dt><span class="sect2"><a href="runtime-config-replication.html#RUNTIME-CONFIG-REPLICATION-SUBSCRIBER">20.6.4. Subscribers</a></span></dt></dl></div><p> + These settings control the behavior of the built-in + <em class="firstterm">streaming replication</em> feature (see + <a class="xref" href="warm-standby.html#STREAMING-REPLICATION" title="27.2.5. Streaming Replication">Section 27.2.5</a>). Servers will be either a + primary or a standby server. Primaries can send data, while standbys + are always receivers of replicated data. When cascading replication + (see <a class="xref" href="warm-standby.html#CASCADING-REPLICATION" title="27.2.7. Cascading Replication">Section 27.2.7</a>) is used, standby servers + can also be senders, as well as receivers. + Parameters are mainly for sending and standby servers, though some + parameters have meaning only on the primary server. Settings may vary + across the cluster without problems if that is required. + </p><div class="sect2" id="RUNTIME-CONFIG-REPLICATION-SENDER"><div class="titlepage"><div><div><h3 class="title">20.6.1. Sending Servers</h3></div></div></div><p> + These parameters can be set on any server that is + to send replication data to one or more standby servers. + The primary is always a sending server, so these parameters must + always be set on the primary. + The role and meaning of these parameters does not change after a + standby becomes the primary. + </p><div class="variablelist"><dl class="variablelist"><dt id="GUC-MAX-WAL-SENDERS"><span class="term"><code class="varname">max_wal_senders</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.3.3.1.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies the maximum number of concurrent connections from standby + servers or streaming base backup clients (i.e., the maximum number of + simultaneously running WAL sender processes). The default is + <code class="literal">10</code>. The value <code class="literal">0</code> means + replication is disabled. Abrupt disconnection of a streaming client might + leave an orphaned connection slot behind until a timeout is reached, + so this parameter should be set slightly higher than the maximum + number of expected clients so disconnected clients can immediately + reconnect. This parameter can only be set at server start. Also, + <code class="varname">wal_level</code> must be set to + <code class="literal">replica</code> or higher to allow connections from standby + servers. + </p><p> + When running a standby server, you must set this parameter to the + same or higher value than on the primary server. Otherwise, queries + will not be allowed in the standby server. + </p></dd><dt id="GUC-MAX-REPLICATION-SLOTS"><span class="term"><code class="varname">max_replication_slots</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.3.3.2.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies the maximum number of replication slots + (see <a class="xref" href="warm-standby.html#STREAMING-REPLICATION-SLOTS" title="27.2.6. Replication Slots">Section 27.2.6</a>) that the server + can support. The default is 10. This parameter can only be set at + server start. + Setting it to a lower value than the number of currently + existing replication slots will prevent the server from starting. + Also, <code class="varname">wal_level</code> must be set + to <code class="literal">replica</code> or higher to allow replication slots to + be used. + </p><p> + On the subscriber side, specifies how many replication origins (see + <a class="xref" href="replication-origins.html" title="Chapter 50. Replication Progress Tracking">Chapter 50</a>) can be tracked simultaneously, + effectively limiting how many logical replication subscriptions can + be created on the server. Setting it to a lower value than the current + number of tracked replication origins (reflected in + <a class="link" href="view-pg-replication-origin-status.html" title="54.18. pg_replication_origin_status">pg_replication_origin_status</a>, + not <a class="link" href="catalog-pg-replication-origin.html" title="53.44. pg_replication_origin">pg_replication_origin</a>) + will prevent the server from starting. + </p></dd><dt id="GUC-WAL-KEEP-SIZE"><span class="term"><code class="varname">wal_keep_size</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.3.3.3.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies the minimum size of past log file segments kept in the + <code class="filename">pg_wal</code> + directory, in case a standby server needs to fetch them for streaming + replication. If a standby + server connected to the sending server falls behind by more than + <code class="varname">wal_keep_size</code> megabytes, the sending server might + remove a WAL segment still needed by the standby, in which case the + replication connection will be terminated. Downstream connections + will also eventually fail as a result. (However, the standby + server can recover by fetching the segment from archive, if WAL + archiving is in use.) + </p><p> + This sets only the minimum size of segments retained in + <code class="filename">pg_wal</code>; the system might need to retain more segments + for WAL archival or to recover from a checkpoint. If + <code class="varname">wal_keep_size</code> is zero (the default), the system + doesn't keep any extra segments for standby purposes, so the number + of old WAL segments available to standby servers is a function of + the location of the previous checkpoint and status of WAL + archiving. + If this value is specified without units, it is taken as megabytes. + This parameter can only be set in the + <code class="filename">postgresql.conf</code> file or on the server command line. + </p></dd><dt id="GUC-MAX-SLOT-WAL-KEEP-SIZE"><span class="term"><code class="varname">max_slot_wal_keep_size</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.3.3.4.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specify the maximum size of WAL files + that <a class="link" href="warm-standby.html#STREAMING-REPLICATION-SLOTS" title="27.2.6. Replication Slots">replication + slots</a> are allowed to retain in the <code class="filename">pg_wal</code> + directory at checkpoint time. + If <code class="varname">max_slot_wal_keep_size</code> is -1 (the default), + replication slots may retain an unlimited amount of WAL files. Otherwise, if + restart_lsn of a replication slot falls behind the current LSN by more + than the given size, the standby using the slot may no longer be able + to continue replication due to removal of required WAL files. You + can see the WAL availability of replication slots + in <a class="link" href="view-pg-replication-slots.html" title="54.19. pg_replication_slots">pg_replication_slots</a>. + If this value is specified without units, it is taken as megabytes. + This parameter can only be set in the <code class="filename">postgresql.conf</code> + file or on the server command line. + </p></dd><dt id="GUC-WAL-SENDER-TIMEOUT"><span class="term"><code class="varname">wal_sender_timeout</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.3.3.5.1.3" class="indexterm"></a> + </span></dt><dd><p> + Terminate replication connections that are inactive for longer + than this amount of time. This is useful for + the sending server to detect a standby crash or network outage. + If this value is specified without units, it is taken as milliseconds. + The default value is 60 seconds. + A value of zero disables the timeout mechanism. + </p><p> + With a cluster distributed across multiple geographic + locations, using different values per location brings more flexibility + in the cluster management. A smaller value is useful for faster + failure detection with a standby having a low-latency network + connection, and a larger value helps in judging better the health + of a standby if located on a remote location, with a high-latency + network connection. + </p></dd><dt id="GUC-TRACK-COMMIT-TIMESTAMP"><span class="term"><code class="varname">track_commit_timestamp</code> (<code class="type">boolean</code>) + <a id="id-1.6.7.9.3.3.6.1.3" class="indexterm"></a> + </span></dt><dd><p> + Record commit time of transactions. This parameter + can only be set in <code class="filename">postgresql.conf</code> file or on the server + command line. The default value is <code class="literal">off</code>. + </p></dd></dl></div></div><div class="sect2" id="RUNTIME-CONFIG-REPLICATION-PRIMARY"><div class="titlepage"><div><div><h3 class="title">20.6.2. Primary Server</h3></div></div></div><p> + These parameters can be set on the primary server that is + to send replication data to one or more standby servers. + Note that in addition to these parameters, + <a class="xref" href="runtime-config-wal.html#GUC-WAL-LEVEL">wal_level</a> must be set appropriately on the primary + server, and optionally WAL archiving can be enabled as + well (see <a class="xref" href="runtime-config-wal.html#RUNTIME-CONFIG-WAL-ARCHIVING" title="20.5.3. Archiving">Section 20.5.3</a>). + The values of these parameters on standby servers are irrelevant, + although you may wish to set them there in preparation for the + possibility of a standby becoming the primary. + </p><div class="variablelist"><dl class="variablelist"><dt id="GUC-SYNCHRONOUS-STANDBY-NAMES"><span class="term"><code class="varname">synchronous_standby_names</code> (<code class="type">string</code>) + <a id="id-1.6.7.9.4.3.1.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies a list of standby servers that can support + <em class="firstterm">synchronous replication</em>, as described in + <a class="xref" href="warm-standby.html#SYNCHRONOUS-REPLICATION" title="27.2.8. Synchronous Replication">Section 27.2.8</a>. + There will be one or more active synchronous standbys; + transactions waiting for commit will be allowed to proceed after + these standby servers confirm receipt of their data. + The synchronous standbys will be those whose names appear + in this list, and + that are both currently connected and streaming data in real-time + (as shown by a state of <code class="literal">streaming</code> in the + <a class="link" href="monitoring-stats.html#MONITORING-PG-STAT-REPLICATION-VIEW" title="28.2.4. pg_stat_replication"> + <code class="structname">pg_stat_replication</code></a> view). + Specifying more than one synchronous standby can allow for very high + availability and protection against data loss. + </p><p> + The name of a standby server for this purpose is the + <code class="varname">application_name</code> setting of the standby, as set in the + standby's connection information. In case of a physical replication + standby, this should be set in the <code class="varname">primary_conninfo</code> + setting; the default is the setting of <a class="xref" href="runtime-config-logging.html#GUC-CLUSTER-NAME">cluster_name</a> + if set, else <code class="literal">walreceiver</code>. + For logical replication, this can be set in the connection + information of the subscription, and it defaults to the + subscription name. For other replication stream consumers, + consult their documentation. + </p><p> + This parameter specifies a list of standby servers using + either of the following syntaxes: +</p><pre class="synopsis"> +[FIRST] <em class="replaceable"><code>num_sync</code></em> ( <em class="replaceable"><code>standby_name</code></em> [, ...] ) +ANY <em class="replaceable"><code>num_sync</code></em> ( <em class="replaceable"><code>standby_name</code></em> [, ...] ) +<em class="replaceable"><code>standby_name</code></em> [, ...] +</pre><p> + where <em class="replaceable"><code>num_sync</code></em> is + the number of synchronous standbys that transactions need to + wait for replies from, + and <em class="replaceable"><code>standby_name</code></em> + is the name of a standby server. + <code class="literal">FIRST</code> and <code class="literal">ANY</code> specify the method to choose + synchronous standbys from the listed servers. + </p><p> + The keyword <code class="literal">FIRST</code>, coupled with + <em class="replaceable"><code>num_sync</code></em>, specifies a + priority-based synchronous replication and makes transaction commits + wait until their WAL records are replicated to + <em class="replaceable"><code>num_sync</code></em> synchronous + standbys chosen based on their priorities. For example, a setting of + <code class="literal">FIRST 3 (s1, s2, s3, s4)</code> will cause each commit to wait for + replies from three higher-priority standbys chosen from standby servers + <code class="literal">s1</code>, <code class="literal">s2</code>, <code class="literal">s3</code> and <code class="literal">s4</code>. + The standbys whose names appear earlier in the list are given higher + priority and will be considered as synchronous. Other standby servers + appearing later in this list represent potential synchronous standbys. + If any of the current synchronous standbys disconnects for whatever + reason, it will be replaced immediately with the next-highest-priority + standby. The keyword <code class="literal">FIRST</code> is optional. + </p><p> + The keyword <code class="literal">ANY</code>, coupled with + <em class="replaceable"><code>num_sync</code></em>, specifies a + quorum-based synchronous replication and makes transaction commits + wait until their WAL records are replicated to <span class="emphasis"><em>at least</em></span> + <em class="replaceable"><code>num_sync</code></em> listed standbys. + For example, a setting of <code class="literal">ANY 3 (s1, s2, s3, s4)</code> will cause + each commit to proceed as soon as at least any three standbys of + <code class="literal">s1</code>, <code class="literal">s2</code>, <code class="literal">s3</code> and <code class="literal">s4</code> + reply. + </p><p> + <code class="literal">FIRST</code> and <code class="literal">ANY</code> are case-insensitive. If these + keywords are used as the name of a standby server, + its <em class="replaceable"><code>standby_name</code></em> must + be double-quoted. + </p><p> + The third syntax was used before <span class="productname">PostgreSQL</span> + version 9.6 and is still supported. It's the same as the first syntax + with <code class="literal">FIRST</code> and + <em class="replaceable"><code>num_sync</code></em> equal to 1. + For example, <code class="literal">FIRST 1 (s1, s2)</code> and <code class="literal">s1, s2</code> have + the same meaning: either <code class="literal">s1</code> or <code class="literal">s2</code> is chosen + as a synchronous standby. + </p><p> + The special entry <code class="literal">*</code> matches any standby name. + </p><p> + There is no mechanism to enforce uniqueness of standby names. In case + of duplicates one of the matching standbys will be considered as + higher priority, though exactly which one is indeterminate. + </p><div class="note"><h3 class="title">Note</h3><p> + Each <em class="replaceable"><code>standby_name</code></em> + should have the form of a valid SQL identifier, unless it + is <code class="literal">*</code>. You can use double-quoting if necessary. But note + that <em class="replaceable"><code>standby_name</code></em>s are + compared to standby application names case-insensitively, whether + double-quoted or not. + </p></div><p> + If no synchronous standby names are specified here, then synchronous + replication is not enabled and transaction commits will not wait for + replication. This is the default configuration. Even when + synchronous replication is enabled, individual transactions can be + configured not to wait for replication by setting the + <a class="xref" href="runtime-config-wal.html#GUC-SYNCHRONOUS-COMMIT">synchronous_commit</a> parameter to + <code class="literal">local</code> or <code class="literal">off</code>. + </p><p> + This parameter can only be set in the <code class="filename">postgresql.conf</code> + file or on the server command line. + </p></dd><dt id="GUC-VACUUM-DEFER-CLEANUP-AGE"><span class="term"><code class="varname">vacuum_defer_cleanup_age</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.4.3.2.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies the number of transactions by which <code class="command">VACUUM</code> and + <a class="link" href="storage-hot.html" title="73.7. Heap-Only Tuples (HOT)"><acronym class="acronym">HOT</acronym> updates</a> + will defer cleanup of dead row versions. The + default is zero transactions, meaning that dead row versions can be + removed as soon as possible, that is, as soon as they are no longer + visible to any open transaction. You may wish to set this to a + non-zero value on a primary server that is supporting hot standby + servers, as described in <a class="xref" href="hot-standby.html" title="27.4. Hot Standby">Section 27.4</a>. This allows + more time for queries on the standby to complete without incurring + conflicts due to early cleanup of rows. However, since the value + is measured in terms of number of write transactions occurring on the + primary server, it is difficult to predict just how much additional + grace time will be made available to standby queries. + This parameter can only be set in the <code class="filename">postgresql.conf</code> + file or on the server command line. + </p><p> + You should also consider setting <code class="varname">hot_standby_feedback</code> + on standby server(s) as an alternative to using this parameter. + </p><p> + This does not prevent cleanup of dead rows which have reached the age + specified by <code class="varname">old_snapshot_threshold</code>. + </p></dd></dl></div></div><div class="sect2" id="RUNTIME-CONFIG-REPLICATION-STANDBY"><div class="titlepage"><div><div><h3 class="title">20.6.3. Standby Servers</h3></div></div></div><p> + These settings control the behavior of a + <a class="link" href="warm-standby.html#STANDBY-SERVER-OPERATION" title="27.2.2. Standby Server Operation">standby server</a> + that is + to receive replication data. Their values on the primary server + are irrelevant. + </p><div class="variablelist"><dl class="variablelist"><dt id="GUC-PRIMARY-CONNINFO"><span class="term"><code class="varname">primary_conninfo</code> (<code class="type">string</code>) + <a id="id-1.6.7.9.5.3.1.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies a connection string to be used for the standby server + to connect with a sending server. This string is in the format + described in <a class="xref" href="libpq-connect.html#LIBPQ-CONNSTRING" title="34.1.1. Connection Strings">Section 34.1.1</a>. If any option is + unspecified in this string, then the corresponding environment + variable (see <a class="xref" href="libpq-envars.html" title="34.15. Environment Variables">Section 34.15</a>) is checked. If the + environment variable is not set either, then + defaults are used. + </p><p> + The connection string should specify the host name (or address) + of the sending server, as well as the port number if it is not + the same as the standby server's default. + Also specify a user name corresponding to a suitably-privileged role + on the sending server (see + <a class="xref" href="warm-standby.html#STREAMING-REPLICATION-AUTHENTICATION" title="27.2.5.1. Authentication">Section 27.2.5.1</a>). + A password needs to be provided too, if the sender demands password + authentication. It can be provided in the + <code class="varname">primary_conninfo</code> string, or in a separate + <code class="filename">~/.pgpass</code> file on the standby server (use + <code class="literal">replication</code> as the database name). + Do not specify a database name in the + <code class="varname">primary_conninfo</code> string. + </p><p> + This parameter can only be set in the <code class="filename">postgresql.conf</code> + file or on the server command line. + If this parameter is changed while the WAL receiver process is + running, that process is signaled to shut down and expected to + restart with the new setting (except if <code class="varname">primary_conninfo</code> + is an empty string). + This setting has no effect if the server is not in standby mode. + </p></dd><dt id="GUC-PRIMARY-SLOT-NAME"><span class="term"><code class="varname">primary_slot_name</code> (<code class="type">string</code>) + <a id="id-1.6.7.9.5.3.2.1.3" class="indexterm"></a> + </span></dt><dd><p> + Optionally specifies an existing replication slot to be used when + connecting to the sending server via streaming replication to control + resource removal on the upstream node + (see <a class="xref" href="warm-standby.html#STREAMING-REPLICATION-SLOTS" title="27.2.6. Replication Slots">Section 27.2.6</a>). + This parameter can only be set in the <code class="filename">postgresql.conf</code> + file or on the server command line. + If this parameter is changed while the WAL receiver process is running, + that process is signaled to shut down and expected to restart with the + new setting. + This setting has no effect if <code class="varname">primary_conninfo</code> is not + set or the server is not in standby mode. + </p></dd><dt id="GUC-PROMOTE-TRIGGER-FILE"><span class="term"><code class="varname">promote_trigger_file</code> (<code class="type">string</code>) + <a id="id-1.6.7.9.5.3.3.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies a trigger file whose presence ends recovery in the + standby. Even if this value is not set, you can still promote + the standby using <code class="command">pg_ctl promote</code> or calling + <code class="function">pg_promote()</code>. + This parameter can only be set in the <code class="filename">postgresql.conf</code> + file or on the server command line. + </p></dd><dt id="GUC-HOT-STANDBY"><span class="term"><code class="varname">hot_standby</code> (<code class="type">boolean</code>) + <a id="id-1.6.7.9.5.3.4.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies whether or not you can connect and run queries during + recovery, as described in <a class="xref" href="hot-standby.html" title="27.4. Hot Standby">Section 27.4</a>. + The default value is <code class="literal">on</code>. + This parameter can only be set at server start. It only has effect + during archive recovery or in standby mode. + </p></dd><dt id="GUC-MAX-STANDBY-ARCHIVE-DELAY"><span class="term"><code class="varname">max_standby_archive_delay</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.5.3.5.1.3" class="indexterm"></a> + </span></dt><dd><p> + When hot standby is active, this parameter determines how long the + standby server should wait before canceling standby queries that + conflict with about-to-be-applied WAL entries, as described in + <a class="xref" href="hot-standby.html#HOT-STANDBY-CONFLICT" title="27.4.2. Handling Query Conflicts">Section 27.4.2</a>. + <code class="varname">max_standby_archive_delay</code> applies when WAL data is + being read from WAL archive (and is therefore not current). + If this value is specified without units, it is taken as milliseconds. + The default is 30 seconds. + A value of -1 allows the standby to wait forever for conflicting + queries to complete. + This parameter can only be set in the <code class="filename">postgresql.conf</code> + file or on the server command line. + </p><p> + Note that <code class="varname">max_standby_archive_delay</code> is not the same as the + maximum length of time a query can run before cancellation; rather it + is the maximum total time allowed to apply any one WAL segment's data. + Thus, if one query has resulted in significant delay earlier in the + WAL segment, subsequent conflicting queries will have much less grace + time. + </p></dd><dt id="GUC-MAX-STANDBY-STREAMING-DELAY"><span class="term"><code class="varname">max_standby_streaming_delay</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.5.3.6.1.3" class="indexterm"></a> + </span></dt><dd><p> + When hot standby is active, this parameter determines how long the + standby server should wait before canceling standby queries that + conflict with about-to-be-applied WAL entries, as described in + <a class="xref" href="hot-standby.html#HOT-STANDBY-CONFLICT" title="27.4.2. Handling Query Conflicts">Section 27.4.2</a>. + <code class="varname">max_standby_streaming_delay</code> applies when WAL data is + being received via streaming replication. + If this value is specified without units, it is taken as milliseconds. + The default is 30 seconds. + A value of -1 allows the standby to wait forever for conflicting + queries to complete. + This parameter can only be set in the <code class="filename">postgresql.conf</code> + file or on the server command line. + </p><p> + Note that <code class="varname">max_standby_streaming_delay</code> is not the same as + the maximum length of time a query can run before cancellation; rather + it is the maximum total time allowed to apply WAL data once it has + been received from the primary server. Thus, if one query has + resulted in significant delay, subsequent conflicting queries will + have much less grace time until the standby server has caught up + again. + </p></dd><dt id="GUC-WAL-RECEIVER-CREATE-TEMP-SLOT"><span class="term"><code class="varname">wal_receiver_create_temp_slot</code> (<code class="type">boolean</code>) + <a id="id-1.6.7.9.5.3.7.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies whether the WAL receiver process should create a temporary replication + slot on the remote instance when no permanent replication slot to use + has been configured (using <a class="xref" href="runtime-config-replication.html#GUC-PRIMARY-SLOT-NAME">primary_slot_name</a>). + The default is off. This parameter can only be set in the + <code class="filename">postgresql.conf</code> file or on the server command line. + If this parameter is changed while the WAL receiver process is running, + that process is signaled to shut down and expected to restart with + the new setting. + </p></dd><dt id="GUC-WAL-RECEIVER-STATUS-INTERVAL"><span class="term"><code class="varname">wal_receiver_status_interval</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.5.3.8.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies the minimum frequency for the WAL receiver + process on the standby to send information about replication progress + to the primary or upstream standby, where it can be seen using the + <a class="link" href="monitoring-stats.html#MONITORING-PG-STAT-REPLICATION-VIEW" title="28.2.4. pg_stat_replication"> + <code class="structname">pg_stat_replication</code></a> + view. The standby will report + the last write-ahead log location it has written, the last position it + has flushed to disk, and the last position it has applied. + This parameter's value is the maximum amount of time between reports. + Updates are sent each time the write or flush positions change, or as + often as specified by this parameter if set to a non-zero value. + There are additional cases where updates are sent while ignoring this + parameter; for example, when processing of the existing WAL completes + or when <code class="varname">synchronous_commit</code> is set to + <code class="literal">remote_apply</code>. + Thus, the apply position may lag slightly behind the true position. + If this value is specified without units, it is taken as seconds. + The default value is 10 seconds. This parameter can only be set in + the <code class="filename">postgresql.conf</code> file or on the server + command line. + </p></dd><dt id="GUC-HOT-STANDBY-FEEDBACK"><span class="term"><code class="varname">hot_standby_feedback</code> (<code class="type">boolean</code>) + <a id="id-1.6.7.9.5.3.9.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies whether or not a hot standby will send feedback to the primary + or upstream standby + about queries currently executing on the standby. This parameter can + be used to eliminate query cancels caused by cleanup records, but + can cause database bloat on the primary for some workloads. + Feedback messages will not be sent more frequently than once per + <code class="varname">wal_receiver_status_interval</code>. The default value is + <code class="literal">off</code>. This parameter can only be set in the + <code class="filename">postgresql.conf</code> file or on the server command line. + </p><p> + If cascaded replication is in use the feedback is passed upstream + until it eventually reaches the primary. Standbys make no other use + of feedback they receive other than to pass upstream. + </p><p> + This setting does not override the behavior of + <code class="varname">old_snapshot_threshold</code> on the primary; a snapshot on the + standby which exceeds the primary's age threshold can become invalid, + resulting in cancellation of transactions on the standby. This is + because <code class="varname">old_snapshot_threshold</code> is intended to provide an + absolute limit on the time which dead rows can contribute to bloat, + which would otherwise be violated because of the configuration of a + standby. + </p></dd><dt id="GUC-WAL-RECEIVER-TIMEOUT"><span class="term"><code class="varname">wal_receiver_timeout</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.5.3.10.1.3" class="indexterm"></a> + </span></dt><dd><p> + Terminate replication connections that are inactive for longer + than this amount of time. This is useful for + the receiving standby server to detect a primary node crash or network + outage. + If this value is specified without units, it is taken as milliseconds. + The default value is 60 seconds. + A value of zero disables the timeout mechanism. + This parameter can only be set in + the <code class="filename">postgresql.conf</code> file or on the server + command line. + </p></dd><dt id="GUC-WAL-RETRIEVE-RETRY-INTERVAL"><span class="term"><code class="varname">wal_retrieve_retry_interval</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.5.3.11.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies how long the standby server should wait when WAL data is not + available from any sources (streaming replication, + local <code class="filename">pg_wal</code> or WAL archive) before trying + again to retrieve WAL data. + If this value is specified without units, it is taken as milliseconds. + The default value is 5 seconds. + This parameter can only be set in + the <code class="filename">postgresql.conf</code> file or on the server + command line. + </p><p> + This parameter is useful in configurations where a node in recovery + needs to control the amount of time to wait for new WAL data to be + available. For example, in archive recovery, it is possible to + make the recovery more responsive in the detection of a new WAL + log file by reducing the value of this parameter. On a system with + low WAL activity, increasing it reduces the amount of requests necessary + to access WAL archives, something useful for example in cloud + environments where the number of times an infrastructure is accessed + is taken into account. + </p></dd><dt id="GUC-RECOVERY-MIN-APPLY-DELAY"><span class="term"><code class="varname">recovery_min_apply_delay</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.5.3.12.1.3" class="indexterm"></a> + </span></dt><dd><p> + By default, a standby server restores WAL records from the + sending server as soon as possible. It may be useful to have a time-delayed + copy of the data, offering opportunities to correct data loss errors. + This parameter allows you to delay recovery by a specified amount + of time. For example, if + you set this parameter to <code class="literal">5min</code>, the standby will + replay each transaction commit only when the system time on the standby + is at least five minutes past the commit time reported by the primary. + If this value is specified without units, it is taken as milliseconds. + The default is zero, adding no delay. + </p><p> + It is possible that the replication delay between servers exceeds the + value of this parameter, in which case no delay is added. + Note that the delay is calculated between the WAL time stamp as written + on primary and the current time on the standby. Delays in transfer + because of network lag or cascading replication configurations + may reduce the actual wait time significantly. If the system + clocks on primary and standby are not synchronized, this may lead to + recovery applying records earlier than expected; but that is not a + major issue because useful settings of this parameter are much larger + than typical time deviations between servers. + </p><p> + The delay occurs only on WAL records for transaction commits. + Other records are replayed as quickly as possible, which + is not a problem because MVCC visibility rules ensure their effects + are not visible until the corresponding commit record is applied. + </p><p> + The delay occurs once the database in recovery has reached a consistent + state, until the standby is promoted or triggered. After that the standby + will end recovery without further waiting. + </p><p> + WAL records must be kept on the standby until they are ready to be + applied. Therefore, longer delays will result in a greater accumulation + of WAL files, increasing disk space requirements for the standby's + <code class="filename">pg_wal</code> directory. + </p><p> + This parameter is intended for use with streaming replication deployments; + however, if the parameter is specified it will be honored in all cases + except crash recovery. + + <code class="varname">hot_standby_feedback</code> will be delayed by use of this feature + which could lead to bloat on the primary; use both together with care. + + </p><div class="warning"><h3 class="title">Warning</h3><p> + Synchronous replication is affected by this setting when <code class="varname">synchronous_commit</code> + is set to <code class="literal">remote_apply</code>; every <code class="literal">COMMIT</code> + will need to wait to be applied. + </p></div><p> + </p><p> + This parameter can only be set in the <code class="filename">postgresql.conf</code> + file or on the server command line. + </p></dd></dl></div></div><div class="sect2" id="RUNTIME-CONFIG-REPLICATION-SUBSCRIBER"><div class="titlepage"><div><div><h3 class="title">20.6.4. Subscribers</h3></div></div></div><p> + These settings control the behavior of a logical replication subscriber. + Their values on the publisher are irrelevant. + </p><p> + Note that <code class="varname">wal_receiver_timeout</code>, + <code class="varname">wal_receiver_status_interval</code> and + <code class="varname">wal_retrieve_retry_interval</code> configuration parameters + affect the logical replication workers as well. + </p><div class="variablelist"><dl class="variablelist"><dt id="GUC-MAX-LOGICAL-REPLICATION-WORKERS"><span class="term"><code class="varname">max_logical_replication_workers</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.6.4.1.1.3" class="indexterm"></a> + </span></dt><dd><p> + Specifies maximum number of logical replication workers. This includes + both apply workers and table synchronization workers. + </p><p> + Logical replication workers are taken from the pool defined by + <code class="varname">max_worker_processes</code>. + </p><p> + The default value is 4. This parameter can only be set at server + start. + </p></dd><dt id="GUC-MAX-SYNC-WORKERS-PER-SUBSCRIPTION"><span class="term"><code class="varname">max_sync_workers_per_subscription</code> (<code class="type">integer</code>) + <a id="id-1.6.7.9.6.4.2.1.3" class="indexterm"></a> + </span></dt><dd><p> + Maximum number of synchronization workers per subscription. This + parameter controls the amount of parallelism of the initial data copy + during the subscription initialization or when new tables are added. + </p><p> + Currently, there can be only one synchronization worker per table. + </p><p> + The synchronization workers are taken from the pool defined by + <code class="varname">max_logical_replication_workers</code>. + </p><p> + The default value is 2. This parameter can only be set in the + <code class="filename">postgresql.conf</code> file or on the server command + line. + </p></dd></dl></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="runtime-config-wal.html" title="20.5. Write Ahead Log">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="runtime-config.html" title="Chapter 20. Server Configuration">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="runtime-config-query.html" title="20.7. Query Planning">Next</a></td></tr><tr><td width="40%" align="left" valign="top">20.5. Write Ahead Log </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 20.7. Query Planning</td></tr></table></div></body></html>
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