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diff --git a/doc/src/sgml/pgsurgery.sgml b/doc/src/sgml/pgsurgery.sgml new file mode 100644 index 0000000..29bccd7 --- /dev/null +++ b/doc/src/sgml/pgsurgery.sgml @@ -0,0 +1,107 @@ +<!-- doc/src/sgml/pgsurgery.sgml --> + +<sect1 id="pgsurgery" xreflabel="pg_surgery"> + <title>pg_surgery — perform low-level surgery on relation data</title> + + <indexterm zone="pgsurgery"> + <primary>pg_surgery</primary> + </indexterm> + + <para> + The <filename>pg_surgery</filename> module provides various functions to + perform surgery on a damaged relation. These functions are unsafe by design + and using them may corrupt (or further corrupt) your database. For example, + these functions can easily be used to make a table inconsistent with its + own indexes, to cause <literal>UNIQUE</literal> or + <literal>FOREIGN KEY</literal> constraint violations, or even to make + tuples visible which, when read, will cause a database server crash. + They should be used with great caution and only as a last resort. + </para> + + <sect2 id="pgsurgery-funcs"> + <title>Functions</title> + + <variablelist> + <varlistentry> + <term> + <function>heap_force_kill(regclass, tid[]) returns void</function> + </term> + + <listitem> + <para> + <function>heap_force_kill</function> marks <quote>used</quote> line + pointers as <quote>dead</quote> without examining the tuples. The + intended use of this function is to forcibly remove tuples that are not + otherwise accessible. For example: +<programlisting> +test=> select * from t1 where ctid = '(0, 1)'; +ERROR: could not access status of transaction 4007513275 +DETAIL: Could not open file "pg_xact/0EED": No such file or directory. + +test=# select heap_force_kill('t1'::regclass, ARRAY['(0, 1)']::tid[]); + heap_force_kill +----------------- + +(1 row) + +test=# select * from t1 where ctid = '(0, 1)'; +(0 rows) + +</programlisting> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>heap_force_freeze(regclass, tid[]) returns void</function> + </term> + + <listitem> + <para> + <function>heap_force_freeze</function> marks tuples as frozen without + examining the tuple data. The intended use of this function is to + make accessible tuples which are inaccessible due to corrupted + visibility information, or which prevent the table from being + successfully vacuumed due to corrupted visibility information. + For example: +<programlisting> +test=> vacuum t1; +ERROR: found xmin 507 from before relfrozenxid 515 +CONTEXT: while scanning block 0 of relation "public.t1" + +test=# select ctid from t1 where xmin = 507; + ctid +------- + (0,3) +(1 row) + +test=# select heap_force_freeze('t1'::regclass, ARRAY['(0, 3)']::tid[]); + heap_force_freeze +------------------- + +(1 row) + +test=# select ctid from t1 where xmin = 2; + ctid +------- + (0,3) +(1 row) + +</programlisting> + </para> + </listitem> + </varlistentry> + + </variablelist> + </sect2> + + <sect2 id="pgsurgery-authors"> + <title>Authors</title> + + <para> + Ashutosh Sharma <email>ashu.coek88@gmail.com</email> + </para> + </sect2> + +</sect1> |