8000 Document pg_get_multixact_members(). · postgres/postgres@0ee7f51 · GitHub
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Document pg_get_multixact_members().
Oversight in commit 0ac5ad5. Author: Sami Imseih <samimseih@gmail.com> Co-authored-by: Álvaro Herrera <alvherre@kurilemu.de> Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> Discussion: https://postgr.es/m/20150619215231.GT133018%40postgresql.org Discussion: https://postgr.es/m/CAA5RZ0sjQDDwJfMRb%3DZ13nDLuRpF13ME2L_BdGxi0op8RKjmDg%40mail.gmail.com Backpatch-through: 13
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‎doc/src/sgml/func.sgml

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@@ -23394,6 +23394,31 @@ SELECT collation for ('foo' COLLATE "de_DE");
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a subtransaction ID.
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>pg_get_multixact_members</primary>
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</indexterm>
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<function>pg_get_multixact_members</function> ( <parameter>multixid</parameter> <type>xid</type> )
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<returnvalue>setof record</returnvalue>
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( <parameter>xid</parameter> <type>xid</type>,
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<parameter>mode</parameter> <type>text</type> )
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</para>
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<para>
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Returns the transaction ID and lock mode for each member of the
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specified multixact ID. The lock modes <literal>forupd</literal>,
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<literal>fornokeyupd</literal>, <literal>sh</literal>, and
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<literal>keysh</literal> correspond to the row-level locks
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<literal>FOR UPDATE</literal>, <literal>FOR NO KEY UPDATE</literal>,
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<literal>FOR SHARE</literal>, and <literal>FOR KEY SHARE</literal>,
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respectively, as described in <xref linkend="locking-rows"/>. Two
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additional modes are specific to multixacts:
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<literal>nokeyupd</literal>, used by updates that do not modify key
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columns, and <literal>upd</literal>, used by updates or deletes that
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modify key columns.
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</para></entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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The internal transaction ID type <type>xid</type> is 32 bits wide and
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wraps around every 4 billion transactions. However,
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the functions shown in <xref linkend="functions-pg-snapshot"/>, except
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<function>age</function> and <function>mxid_age</function>, use a
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<function>age</function>, <function>mxid_age</function>, and
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<function>pg_get_multixact_members</function>, use a
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64-bit type <type>xid8</type> that does not wrap around during the life
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of an installation, and can be converted to <type>xid</type> by casting if
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required. The data type <type>pg_snapshot</type> stores information about

‎doc/src/sgml/maintenance.sgml

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@@ -690,7 +690,10 @@ HINT: Stop the postmaster and vacuum that database in single-user mode.
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careful aging management, storage cleanup, and wraparound handling.
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There is a separate storage area which holds the list of members in
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each multixact, which also uses a 32-bit counter and which must also
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be managed.
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be managed. The system function
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<function>pg_get_multixact_members()</function> described in
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<xref linkend="functions-pg-snapshot"/> can be used to examine the
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transaction IDs associated with a multixact ID.
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</para>
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<para>

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