diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/config.sgml | 23 | ||||
| -rw-r--r-- | doc/src/sgml/monitoring.sgml | 62 | ||||
| -rw-r--r-- | doc/src/sgml/wal.sgml | 29 |
3 files changed, 113 insertions, 1 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 967de73596f..529876895b8 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -7450,7 +7450,7 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv; <listitem> <para> Enables timing of database I/O calls. This parameter is off by - default, because it will repeatedly query the operating system for + default, as it will repeatedly query the operating system for the current time, which may cause significant overhead on some platforms. You can use the <xref linkend="pgtesttiming"/> tool to measure the overhead of timing on your system. @@ -7464,6 +7464,27 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv; </listitem> </varlistentry> + <varlistentry id="guc-track-wal-io-timing" xreflabel="track_wal_io_timing"> + <term><varname>track_wal_io_timing</varname> (<type>boolean</type>) + <indexterm> + <primary><varname>track_wal_io_timing</varname> configuration parameter</primary> + </indexterm> + </term> + <listitem> + <para> + Enables timing of WAL I/O calls. This parameter is off by default, + as it will repeatedly query the operating system for the current time, + which may cause significant overhead on some platforms. + You can use the <application>pg_test_timing</application> tool to + measure the overhead of timing on your system. + I/O timing information is + displayed in <link linkend="monitoring-pg-stat-wal-view"> + <structname>pg_stat_wal</structname></link>. Only superusers can + change this setting. + </para> + </listitem> + </varlistentry> + <varlistentry id="guc-track-functions" xreflabel="track_functions"> <term><varname>track_functions</varname> (<type>enum</type>) <indexterm> diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index 51f73384041..3335d71eba0 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -186,6 +186,11 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser </para> <para> + The parameter <xref linkend="guc-track-wal-io-timing"/> enables monitoring + of WAL write times. + </para> + + <para> Normally these parameters are set in <filename>postgresql.conf</filename> so that they apply to all server processes, but it is possible to turn them on or off in individual sessions using the <xref @@ -3479,6 +3484,63 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i <row> <entry role="catalog_table_entry"><para role="column_definition"> + <structfield>wal_write</structfield> <type>bigint</type> + </para> + <para> + Number of times WAL buffers were written out to disk via + <function>XLogWrite</function> request. + See <xref linkend="wal-configuration"/> for more information about + the internal WAL function <function>XLogWrite</function>. + </para></entry> + </row> + + <row> + <entry role="catalog_table_entry"><para role="column_definition"> + <structfield>wal_sync</structfield> <type>bigint</type> + </para> + <para> + Number of times WAL files were synced to disk via + <function>issue_xlog_fsync</function> request + (if <xref linkend="guc-fsync"/> is <literal>on</literal> and + <xref linkend="guc-wal-sync-method"/> is either + <literal>fdatasync</literal>, <literal>fsync</literal> or + <literal>fsync_writethrough</literal>, otherwise zero). + See <xref linkend="wal-configuration"/> for more information about + the internal WAL function <function>issue_xlog_fsync</function>. + </para></entry> + </row> + + <row> + <entry role="catalog_table_entry"><para role="column_definition"> + <structfield>wal_write_time</structfield> <type>double precision</type> + </para> + <para> + Total amount of time spent writing WAL buffers to disk via + <function>XLogWrite</function> request, in milliseconds + (if <xref linkend="guc-track-wal-io-timing"/> is enabled, + otherwise zero). This includes the sync time when + <varname>wal_sync_method</varname> is either + <literal>open_datasync</literal> or <literal>open_sync</literal>. + </para></entry> + </row> + + <row> + <entry role="catalog_table_entry"><para role="column_definition"> + <structfield>wal_sync_time</structfield> <type>double precision</type> + </para> + <para> + Total amount of time spent syncing WAL files to disk via + <function>issue_xlog_fsync</function> request, in milliseconds + (if <varname>track_wal_io_timing</varname> is enabled, + <varname>fsync</varname> is <literal>on</literal>, and + <varname>wal_sync_method</varname> is either + <literal>fdatasync</literal>, <literal>fsync</literal> or + <literal>fsync_writethrough</literal>, otherwise zero). + </para></entry> + </row> + + <row> + <entry role="catalog_table_entry"><para role="column_definition"> <structfield>stats_reset</structfield> <type>timestamp with time zone</type> </para> <para> diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml index f75527f764a..ae4a3c12931 100644 --- a/doc/src/sgml/wal.sgml +++ b/doc/src/sgml/wal.sgml @@ -767,6 +767,35 @@ <acronym>WAL</acronym> call being logged to the server log. This option might be replaced by a more general mechanism in the future. </para> + + <para> + There are two internal functions to write WAL data to disk: + <function>XLogWrite</function> and <function>issue_xlog_fsync</function>. + When <xref linkend="guc-track-wal-io-timing"/> is enabled, the total + amounts of time <function>XLogWrite</function> writes and + <function>issue_xlog_fsync</function> syncs WAL data to disk are counted as + <literal>wal_write_time</literal> and <literal>wal_sync_time</literal> in + <xref linkend="pg-stat-wal-view"/>, respectively. + <function>XLogWrite</function> is normally called by + <function>XLogInsertRecord</function> (when there is no space for the new + record in WAL buffers), <function>XLogFlush</function> and the WAL writer, + to write WAL buffers to disk and call <function>issue_xlog_fsync</function>. + <function>issue_xlog_fsync</function> is normally called by + <function>XLogWrite</function> to sync WAL files to disk. + If <varname>wal_sync_method</varname> is either + <literal>open_datasync</literal> or <literal>open_sync</literal>, + a write operation in <function>XLogWrite</function> guarantees to sync written + WAL data to disk and <function>issue_xlog_fsync</function> does nothing. + If <varname>wal_sync_method</varname> is either <literal>fdatasync</literal>, + <literal>fsync</literal>, or <literal>fsync_writethrough</literal>, + the write operation moves WAL buffers to kernel cache and + <function>issue_xlog_fsync</function> syncs them to disk. Regardless + of the setting of <varname>track_wal_io_timing</varname>, the numbers + of times <function>XLogWrite</function> writes and + <function>issue_xlog_fsync</function> syncs WAL data to disk are also + counted as <literal>wal_write</literal> and <literal>wal_sync</literal> + in <structname>pg_stat_wal</structname>, respectively. + </para> </sect1> <sect1 id="wal-internals"> |