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The original titles only had the module name, which is not very useful when scanning the list. By adding a very brief description to each title, the table of contents becomes friendlier. Also amend the introduction in the "additional modules" appendix, using the word "Extension" more extensively. Nowadays, almost all contrib modules are extensions, so this is also helpful. Author: Karl O. Pinc <kop@karlpinc.com> Reviewed-by: Brar Piening <brar@gmx.de> Discussion: https://postgr.es/m/20230102180015.372995a9@slate.karlpinc.com
107 lines
2.9 KiB
Text
107 lines
2.9 KiB
Text
<!-- doc/src/sgml/pgsurgery.sgml -->
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<sect1 id="pgsurgery" xreflabel="pg_surgery">
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<title>pg_surgery — perform low-level surgery on relation data</title>
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<indexterm zone="pgsurgery">
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<primary>pg_surgery</primary>
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</indexterm>
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<para>
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The <filename>pg_surgery</filename> module provides various functions to
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perform surgery on a damaged relation. These functions are unsafe by design
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and using them may corrupt (or further corrupt) your database. For example,
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these functions can easily be used to make a table inconsistent with its
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own indexes, to cause <literal>UNIQUE</literal> or
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<literal>FOREIGN KEY</literal> constraint violations, or even to make
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tuples visible which, when read, will cause a database server crash.
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They should be used with great caution and only as a last resort.
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</para>
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<sect2 id="pgsurgery-funcs">
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<title>Functions</title>
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<variablelist>
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<varlistentry>
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<term>
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<function>heap_force_kill(regclass, tid[]) returns void</function>
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</term>
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<listitem>
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<para>
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<function>heap_force_kill</function> marks <quote>used</quote> line
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pointers as <quote>dead</quote> without examining the tuples. The
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intended use of this function is to forcibly remove tuples that are not
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otherwise accessible. For example:
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<programlisting>
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test=> select * from t1 where ctid = '(0, 1)';
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ERROR: could not access status of transaction 4007513275
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DETAIL: Could not open file "pg_xact/0EED": No such file or directory.
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test=# select heap_force_kill('t1'::regclass, ARRAY['(0, 1)']::tid[]);
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heap_force_kill
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-----------------
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(1 row)
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test=# select * from t1 where ctid = '(0, 1)';
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(0 rows)
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</programlisting>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<function>heap_force_freeze(regclass, tid[]) returns void</function>
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</term>
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<listitem>
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<para>
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<function>heap_force_freeze</function> marks tuples as frozen without
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examining the tuple data. The intended use of this function is to
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make accessible tuples which are inaccessible due to corrupted
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visibility information, or which prevent the table from being
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successfully vacuumed due to corrupted visibility information.
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For example:
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<programlisting>
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test=> vacuum t1;
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ERROR: found xmin 507 from before relfrozenxid 515
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CONTEXT: while scanning block 0 of relation "public.t1"
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test=# select ctid from t1 where xmin = 507;
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ctid
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-------
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(0,3)
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(1 row)
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test=# select heap_force_freeze('t1'::regclass, ARRAY['(0, 3)']::tid[]);
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heap_force_freeze
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-------------------
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(1 row)
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test=# select ctid from t1 where xmin = 2;
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ctid
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-------
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(0,3)
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(1 row)
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</programlisting>
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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<sect2 id="pgsurgery-authors">
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<title>Authors</title>
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<para>
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Ashutosh Sharma <email>ashu.coek88@gmail.com</email>
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</para>
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</sect2>
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</sect1>
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