diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/config.sgml | 64 | ||||
| -rw-r--r-- | doc/src/sgml/monitoring.sgml | 86 | ||||
| -rw-r--r-- | doc/src/sgml/wal.sgml | 12 |
3 files changed, 160 insertions, 2 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 6901e71f9d3..ac533968a0c 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -3657,6 +3657,70 @@ include_dir 'conf.d' </variablelist> </sect2> + <sect2 id="runtime-config-wal-recovery"> + + <title>Recovery</title> + + <indexterm> + <primary>configuration</primary> + <secondary>of recovery</secondary> + <tertiary>general settings</tertiary> + </indexterm> + + <para> + This section describes the settings that apply to recovery in general, + affecting crash recovery, streaming replication and archive-based + replication. + </para> + + + <variablelist> + <varlistentry id="guc-recovery-prefetch" xreflabel="recovery_prefetch"> + <term><varname>recovery_prefetch</varname> (<type>enum</type>) + <indexterm> + <primary><varname>recovery_prefetch</varname> configuration parameter</primary> + </indexterm> + </term> + <listitem> + <para> + Whether to try to prefetch blocks that are referenced in the WAL that + are not yet in the buffer pool, during recovery. Valid values are + <literal>off</literal> (the default), <literal>on</literal> and + <literal>try</literal>. The setting <literal>try</literal> enables + prefetching only if the operating system provides the + <function>posix_fadvise</function> function, which is currently used + to implement prefetching. Note that some operating systems provide the + function, but it doesn't do anything. + </para> + <para> + Prefetching blocks that will soon be needed can reduce I/O wait times + during recovery with some workloads. + See also the <xref linkend="guc-wal-decode-buffer-size"/> and + <xref linkend="guc-maintenance-io-concurrency"/> settings, which limit + prefetching activity. + </para> + </listitem> + </varlistentry> + + <varlistentry id="guc-wal-decode-buffer-size" xreflabel="wal_decode_buffer_size"> + <term><varname>wal_decode_buffer_size</varname> (<type>integer</type>) + <indexterm> + <primary><varname>wal_decode_buffer_size</varname> configuration parameter</primary> + </indexterm> + </term> + <listitem> + <para> + A limit on how far ahead the server can look in the WAL, to find + blocks to prefetch. If this value is specified without units, it is + taken as bytes. + The default is 512kB. + </para> + </listitem> + </varlistentry> + + </variablelist> + </sect2> + <sect2 id="runtime-config-wal-archive-recovery"> <title>Archive Recovery</title> diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index 24924647b5f..76766d28dd4 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -329,6 +329,13 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser </row> <row> + <entry><structname>pg_stat_recovery_prefetch</structname><indexterm><primary>pg_stat_recovery_prefetch</primary></indexterm></entry> + <entry>Only one row, showing statistics about blocks prefetched during recovery. + See <xref linkend="pg-stat-recovery-prefetch-view"/> for details. + </entry> + </row> + + <row> <entry><structname>pg_stat_subscription</structname><indexterm><primary>pg_stat_subscription</primary></indexterm></entry> <entry>At least one row per subscription, showing information about the subscription workers. @@ -2979,6 +2986,78 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i copy of the subscribed tables. </para> + <table id="pg-stat-recovery-prefetch-view" xreflabel="pg_stat_recovery_prefetch"> + <title><structname>pg_stat_recovery_prefetch</structname> View</title> + <tgroup cols="3"> + <thead> + <row> + <entry>Column</entry> + <entry>Type</entry> + <entry>Description</entry> + </row> + </thead> + + <tbody> + <row> + <entry><structfield>prefetch</structfield></entry> + <entry><type>bigint</type></entry> + <entry>Number of blocks prefetched because they were not in the buffer pool</entry> + </row> + <row> + <entry><structfield>hit</structfield></entry> + <entry><type>bigint</type></entry> + <entry>Number of blocks not prefetched because they were already in the buffer pool</entry> + </row> + <row> + <entry><structfield>skip_init</structfield></entry> + <entry><type>bigint</type></entry> + <entry>Number of blocks not prefetched because they would be zero-initialized</entry> + </row> + <row> + <entry><structfield>skip_new</structfield></entry> + <entry><type>bigint</type></entry> + <entry>Number of blocks not prefetched because they didn't exist yet</entry> + </row> + <row> + <entry><structfield>skip_fpw</structfield></entry> + <entry><type>bigint</type></entry> + <entry>Number of blocks not prefetched because a full page image was included in the WAL</entry> + </row> + <row> + <entry><structfield>skip_rep</structfield></entry> + <entry><type>bigint</type></entry> + <entry>Number of blocks not prefetched because they were already recently prefetched</entry> + </row> + <row> + <entry><structfield>wal_distance</structfield></entry> + <entry><type>integer</type></entry> + <entry>How many bytes ahead the prefetcher is looking</entry> + </row> + <row> + <entry><structfield>block_distance</structfield></entry> + <entry><type>integer</type></entry> + <entry>How many blocks ahead the prefetcher is looking</entry> + </row> + <row> + <entry><structfield>io_depth</structfield></entry> + <entry><type>integer</type></entry> + <entry>How many prefetches have been initiated but are not yet known to have completed</entry> + </row> + </tbody> + </tgroup> + </table> + + <para> + The <structname>pg_stat_recovery_prefetch</structname> view will contain + only one row. It is filled with nulls if recovery has not run or + <xref linkend="guc-recovery-prefetch"/> is not enabled. The + columns <structfield>wal_distance</structfield>, + <structfield>block_distance</structfield> + and <structfield>io_depth</structfield> show current values, and the + other columns show cumulative counters that can be reset + with the <function>pg_stat_reset_shared</function> function. + </para> + <table id="pg-stat-subscription" xreflabel="pg_stat_subscription"> <title><structname>pg_stat_subscription</structname> View</title> <tgroup cols="1"> @@ -5199,8 +5278,11 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i all the counters shown in the <structname>pg_stat_bgwriter</structname> view, <literal>archiver</literal> to reset all the counters shown in - the <structname>pg_stat_archiver</structname> view or <literal>wal</literal> - to reset all the counters shown in the <structname>pg_stat_wal</structname> view. + the <structname>pg_stat_archiver</structname> view, + <literal>wal</literal> to reset all the counters shown in the + <structname>pg_stat_wal</structname> view or + <literal>recovery_prefetch</literal> to reset all the counters shown + in the <structname>pg_stat_recovery_prefetch</structname> view. </para> <para> This function is restricted to superusers by default, but other users diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml index 2bb27a84682..6b3406b7de6 100644 --- a/doc/src/sgml/wal.sgml +++ b/doc/src/sgml/wal.sgml @@ -803,6 +803,18 @@ counted as <literal>wal_write</literal> and <literal>wal_sync</literal> in <structname>pg_stat_wal</structname>, respectively. </para> + + <para> + The <xref linkend="guc-recovery-prefetch"/> parameter can be used to reduce + I/O wait times during recovery by instructing the kernel to initiate reads + of disk blocks that will soon be needed but are not currently in + <productname>PostgreSQL</productname>'s buffer pool. + The <xref linkend="guc-maintenance-io-concurrency"/> and + <xref linkend="guc-wal-decode-buffer-size"/> settings limit prefetching + concurrency and distance, respectively. By default, it is set to + <literal>try</literal>, which enabled the feature on systems where + <function>posix_fadvise</function> is available. + </para> </sect1> <sect1 id="wal-internals"> |