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Add VACUUM (DISABLE_PAGE_SKIPPING) for emergencies.

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If you really want to vacuum every single page in the relation,
regardless of apparent visibility status or anything else, you can use
this option.  In previous releases, this behavior could be achieved
using VACUUM (FREEZE), but because we can now recognize all-frozen
pages as not needing to be frozen again, that no longer works.  There
should be no need for routine use of this option, but maybe bugs or
disaster recovery will necessitate its use.

Patch by me, reviewed by Andres Freund.
This commit is contained in:
Robert Haas
2016-06-17 15:48:57 -04:00
parent 20eb2731b7
commit ede62e56fb
7 changed files with 97 additions and 46 deletions
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21
doc/src/sgml/ref/vacuum.sgml
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@ -21,7 +21,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
VACUUM [ ( { FULL | FREEZE | VERBOSE | ANALYZE } [, ...] ) ] [ <replaceable class="PARAMETER">table_name</replaceable> [ (<replaceable class="PARAMETER">column_name</replaceable> [, ...] ) ] ]
VACUUM [ ( { FULL | FREEZE | VERBOSE | ANALYZE | DISABLE_PAGE_SKIPPING } [, ...] ) ] [ <replaceable class="PARAMETER">table_name</replaceable> [ (<replaceable class="PARAMETER">column_name</replaceable> [, ...] ) ] ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ <replaceable class="PARAMETER">table_name</replaceable> ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ <replaceable class="PARAMETER">table_name</replaceable> [ (<replaceable class="PARAMETER">column_name</replaceable> [, ...] ) ] ]
</synopsis>
@ -129,6 +129,25 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ <replaceable class="PARAMETER">
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DISABLE_PAGE_SKIPPING</literal></term>
<listitem>
<para>
Normally, <command>VACUUM</> will skip pages based on the <link
linkend="vacuum-for-visibility-map">visibility map</>. Pages where
all tuples are known to be frozen can always be skipped, and those
where all tuples are known to be visible to all transactions may be
skipped except when performing an aggressive vacuum. Furthermore,
except when performing an aggressive vacuum, some pages may be skipped
in order to avoid waiting for other sessions to finish using them.
This option disables all page-skipping behavior, and is intended to
be used only the contents of the visibility map are thought to
be suspect, which should happen only if there is a hardware or software
issue causing database corruption.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">table_name</replaceable></term>
<listitem>