diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/config.sgml | 39 | ||||
| -rw-r--r-- | doc/src/sgml/maintenance.sgml | 33 | ||||
| -rw-r--r-- | doc/src/sgml/ref/create_table.sgml | 15 |
3 files changed, 79 insertions, 8 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 17795616b5d..fc186657a53 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -9147,6 +9147,45 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv; </listitem> </varlistentry> + <varlistentry id="guc-vacuum-max-eager-freeze-failure-rate" xreflabel="vacuum_max_eager_freeze_failure_rate"> + <term><varname>vacuum_max_eager_freeze_failure_rate</varname> (<type>floating point</type>) + <indexterm> + <primary><varname>vacuum_max_eager_freeze_failure_rate</varname> configuration parameter</primary> + </indexterm> + </term> + <listitem> + <para> + Specifies the maximum number of pages (as a fraction of total pages in + the relation) that <command>VACUUM</command> may scan and + <emphasis>fail</emphasis> to set all-frozen in the visibility map + before disabling eager scanning. A value of <literal>0</literal> + disables eager scanning altogether. The default is + <literal>0.03</literal> (3%). + </para> + + <para> + Note that when eager scanning is enabled, successful page freezes do + not count against the cap on eager freeze failures. Successful page + freezes are capped internally at 20% of the all-visible but not + all-frozen pages in the relation. Capping successful page freezes helps + amortize the overhead across multiple normal vacuums and limits the + potential downside of wasted eager freezes of pages that are modified + again before the next aggressive vacuum. + </para> + + <para> + This parameter can only be set in the + <filename>postgresql.conf</filename> file or on the server command + line; but the setting can be overridden for individual tables by + changing the + <link linkend="reloption-vacuum-max-eager-freeze-failure-rate"> + corresponding table storage parameter</link>. + For more information on tuning vacuum's freezing behavior, + see <xref linkend="vacuum-for-wraparound"/>. + </para> + </listitem> + </varlistentry> + </variablelist> </sect2> </sect1> diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml index f84ad7557d9..b5b9da7f8a9 100644 --- a/doc/src/sgml/maintenance.sgml +++ b/doc/src/sgml/maintenance.sgml @@ -496,9 +496,25 @@ When that happens, <command>VACUUM</command> will eventually need to perform an <firstterm>aggressive vacuum</firstterm>, which will freeze all eligible unfrozen XID and MXID values, including those from all-visible but not all-frozen pages. - In practice most tables require periodic aggressive vacuuming. + </para> + + <para> + If a table is building up a backlog of all-visible but not all-frozen + pages, a normal vacuum may choose to scan skippable pages in an effort to + freeze them. Doing so decreases the number of pages the next aggressive + vacuum must scan. These are referred to as <firstterm>eagerly + scanned</firstterm> pages. Eager scanning can be tuned to attempt to freeze + more all-visible pages by increasing <xref + linkend="guc-vacuum-max-eager-freeze-failure-rate"/>. Even if eager + scanning has kept the number of all-visible but not all-frozen pages to a + minimum, most tables still require periodic aggressive vacuuming. However, + any pages successfully eager frozen may be skipped during an aggressive + vacuum, so eager freezing may minimize the overhead of aggressive vacuums. + </para> + + <para> <xref linkend="guc-vacuum-freeze-table-age"/> - controls when <command>VACUUM</command> does that: all-visible but not all-frozen + controls when a table is aggressively vacuumed. All all-visible but not all-frozen pages are scanned if the number of transactions that have passed since the last such scan is greater than <varname>vacuum_freeze_table_age</varname> minus <varname>vacuum_freeze_min_age</varname>. Setting @@ -626,10 +642,12 @@ SELECT datname, age(datfrozenxid) FROM pg_database; </tip> <para> - <command>VACUUM</command> normally only scans pages that have been modified - since the last vacuum, but <structfield>relfrozenxid</structfield> can only be - advanced when every page of the table - that might contain unfrozen XIDs is scanned. This happens when + While <command>VACUUM</command> scans mostly pages that have been + modified since the last vacuum, it may also eagerly scan some + all-visible but not all-frozen pages in an attempt to freeze them, but + the <structfield>relfrozenxid</structfield> will only be advanced when + every page of the table that might contain unfrozen XIDs is scanned. + This happens when <structfield>relfrozenxid</structfield> is more than <varname>vacuum_freeze_table_age</varname> transactions old, when <command>VACUUM</command>'s <literal>FREEZE</literal> option is used, or when all @@ -931,8 +949,7 @@ vacuum insert threshold = vacuum base insert threshold + vacuum insert scale fac If the <structfield>relfrozenxid</structfield> value of the table is more than <varname>vacuum_freeze_table_age</varname> transactions old, an aggressive vacuum is performed to freeze old tuples and advance - <structfield>relfrozenxid</structfield>; otherwise, only pages that have been modified - since the last vacuum are scanned. + <structfield>relfrozenxid</structfield>. </para> <para> diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml index 9acbc4dd34d..0a3e520f215 100644 --- a/doc/src/sgml/ref/create_table.sgml +++ b/doc/src/sgml/ref/create_table.sgml @@ -1950,6 +1950,21 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM </listitem> </varlistentry> + <varlistentry id="reloption-vacuum-max-eager-freeze-failure-rate" xreflabel="vacuum_max_eager_freeze_failure_rate"> + <term><literal>vacuum_max_eager_freeze_failure_rate</literal>, <literal>toast.vacuum_max_eager_freeze_failure_rate</literal> (<type>floating point</type>) + <indexterm> + <primary><varname>vacuum_max_eager_freeze_failure_rate</varname></primary> + <secondary>storage parameter</secondary> + </indexterm> + </term> + <listitem> + <para> + Per-table value for <xref linkend="guc-vacuum-max-eager-freeze-failure-rate"/> + parameter. + </para> + </listitem> + </varlistentry> + <varlistentry id="reloption-user-catalog-table" xreflabel="user_catalog_table"> <term><literal>user_catalog_table</literal> (<type>boolean</type>) <indexterm> |