Separate multixact freezing parameters from xid's

Previously we were piggybacking on transaction ID parameters to freeze
multixacts; but since there isn't necessarily any relationship between
rates of Xid and multixact consumption, this turns out not to be a good
idea.

Therefore, we now have multixact-specific freezing parameters:

vacuum_multixact_freeze_min_age: when to remove multis as we come across
them in vacuum (default to 5 million, i.e. early in comparison to Xid's
default of 50 million)

vacuum_multixact_freeze_table_age: when to force whole-table scans
instead of scanning only the pages marked as not all visible in
visibility map (default to 150 million, same as for Xids).  Whichever of
both which reaches the 150 million mark earlier will cause a whole-table
scan.

autovacuum_multixact_freeze_max_age: when for cause emergency,
uninterruptible whole-table scans (default to 400 million, double as
that for Xids).  This means there shouldn't be more frequent emergency
vacuuming than previously, unless multixacts are being used very
rapidly.

Backpatch to 9.3 where multixacts were made to persist enough to require
freezing.  To avoid an ABI break in 9.3, VacuumStmt has a couple of
fields in an unnatural place, and StdRdOptions is split in two so that
the newly added fields can go at the end.

Patch by me, reviewed by Robert Haas, with additional input from Andres
Freund and Tom Lane.

1 files changed, 38 insertions, 1 deletions

diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index e0b8a4ecaf..7a01c63d5f 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -985,7 +985,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
      <para>
      Custom <xref linkend="guc-vacuum-freeze-min-age"> parameter. Note that
      autovacuum will ignore attempts to set a per-table
-     <literal>autovacuum_freeze_min_age</> larger than the half system-wide
+     <literal>autovacuum_freeze_min_age</> larger than half the system-wide
      <xref linkend="guc-autovacuum-freeze-max-age"> setting.
      </para>
     </listitem>
@@ -1014,6 +1014,43 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>autovacuum_multixact_freeze_min_age</literal>, <literal>toast.autovacuum_multixact_freeze_min_age</literal> (<type>integer</type>)</term>
+    <listitem>
+     <para>
+      Custom <xref linkend="guc-vacuum-multixact-freeze-min-age"> parameter.
+      Note that autovacuum will ignore attempts to set a per-table
+      <literal>autovacuum_multixact_freeze_min_age</> larger than half the
+      system-wide <xref linkend="guc-autovacuum-multixact-freeze-max-age">
+      setting.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>autovacuum_multixact_freeze_max_age</literal>, <literal>toast.autovacuum_multixact_freeze_max_age</literal> (<type>integer</type>)</term>
+    <listitem>
+     <para>
+      Custom <xref linkend="guc-autovacuum-multixact-freeze-max-age"> parameter. Note
+      that autovacuum will ignore attempts to set a per-table
+      <literal>autovacuum_multixact_freeze_max_age</> larger than the
+      system-wide setting (it can only be set smaller).  Note that while you
+      can set <literal>autovacuum_multixact_freeze_max_age</> very small,
+      or even zero, this is usually unwise since it will force frequent
+      vacuuming.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>autovacuum_multixact_freeze_table_age</literal>, <literal>toast.autovacuum_multixact_freeze_table_age</literal> (<type>integer</type>)</term>
+    <listitem>
+     <para>
+      Custom <xref linkend="guc-vacuum-multixact-freeze-table-age"> parameter.
+     </para>
+    </listitem>
+   </varlistentry>
+
    </variablelist>
 
   </refsect2>