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Move most /contrib README files into SGML. Some still need conversion

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Bruce Momjian
2007-11-10 23:30:46 +00:00
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<sect1 id="pgstattuple">
<title>pgstattuple</title>
<indexterm zone="pgstattuple">
<primary>pgstattuple</primary>
</indexterm>
<para>
<literal>pgstattuple</literal> modules provides various functions to obtain
tuple statistics.
</para>
<sect2>
<title>Functions</title>
<itemizedlist>
<listitem>
<para>
<literal>pgstattuple()</literal> returns the relation length, percentage
of the "dead" tuples of a relation and other info. This may help users to
determine whether vacuum is necessary or not. Here is an example session:
</para>
<programlisting>
test=> \x
Expanded display is on.
test=> SELECT * FROM pgstattuple('pg_catalog.pg_proc');
-[ RECORD 1 ]------+-------
table_len | 458752
tuple_count | 1470
tuple_len | 438896
tuple_percent | 95.67
dead_tuple_count | 11
dead_tuple_len | 3157
dead_tuple_percent | 0.69
free_space | 8932
free_percent | 1.95
</programlisting>
<para>
Here are explanations for each column:
</para>
<table>
<title><literal>pgstattuple()</literal> column descriptions</title>
<tgroup cols="2">
<thead>
<row>
<entry>Column</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>table_len</entry>
<entry>physical relation length in bytes</entry>
</row>
<row>
<entry>tuple_count</entry>
<entry>number of live tuples</entry>
</row>
<row>
<entry>tuple_len</entry>
<entry>total tuples length in bytes</entry>
</row>
<row>
<entry>tuple_percent</entry>
<entry>live tuples in %</entry>
</row>
<row>
<entry>dead_tuple_len</entry>
<entry>total dead tuples length in bytes</entry>
</row>
<row>
<entry>dead_tuple_percent</entry>
<entry>dead tuples in %</entry>
</row>
<row>
<entry>free_space</entry>
<entry>free space in bytes</entry>
</row>
<row>
<entry>free_percent</entry>
<entry>free space in %</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<note>
<para>
<literal>pgstattuple</literal> acquires only a read lock on the relation. So
concurrent update may affect the result.
</para>
</note>
<note>
<para>
<literal>pgstattuple</literal> judges a tuple is "dead" if HeapTupleSatisfiesNow()
returns false.
</para>
</note>
</para>
</listitem>
<listitem>
<para>
<literal>pg_relpages()</literal> returns the number of pages in the relation.
</para>
</listitem>
<listitem>
<para>
<literal>pgstatindex()</literal> returns an array showing the information about an index:
</para>
<programlisting>
test=> \x
Expanded display is on.
test=> SELECT * FROM pgstatindex('pg_cast_oid_index');
-[ RECORD 1 ]------+------
version | 2
tree_level | 0
index_size | 8192
root_block_no | 1
internal_pages | 0
leaf_pages | 1
empty_pages | 0
deleted_pages | 0
avg_leaf_density | 50.27
leaf_fragmentation | 0
</programlisting>
</listitem>
</itemizedlist>
</sect2>
<sect2>
<title>Usage</title>
<para>
<literal>pgstattuple</literal> may be called as a relation function and is
defined as follows:
</para>
<programlisting>
CREATE OR REPLACE FUNCTION pgstattuple(text) RETURNS pgstattuple_type
AS 'MODULE_PATHNAME', 'pgstattuple'
LANGUAGE C STRICT;
CREATE OR REPLACE FUNCTION pgstattuple(oid) RETURNS pgstattuple_type
AS 'MODULE_PATHNAME', 'pgstattuplebyid'
LANGUAGE C STRICT;
</programlisting>
<para>
The argument is the relation name (optionally it may be qualified)
or the OID of the relation. Note that pgstattuple only returns
one row.
</para>
</sect2>
</sect1>