275 lines
7.2 KiB
Plaintext
275 lines
7.2 KiB
Plaintext
<!-- $PostgreSQL: pgsql/doc/src/sgml/pgstattuple.sgml,v 1.4 2008/03/21 03:23:30 tgl Exp $ -->
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<sect1 id="pgstattuple">
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<title>pgstattuple</title>
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<indexterm zone="pgstattuple">
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<primary>pgstattuple</primary>
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</indexterm>
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<para>
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The <filename>pgstattuple</filename> module provides various functions to
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obtain tuple-level statistics.
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</para>
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<sect2>
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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>pgstattuple(text) returns record</>
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</term>
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<listitem>
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<para>
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<function>pgstattuple</function> returns a relation's physical length,
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percentage of <quote>dead</> tuples, and other info. This may help users
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to determine whether vacuum is necessary or not. The argument is the
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target relation's name (optionally schema-qualified).
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For example:
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</para>
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<programlisting>
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test=> SELECT * FROM pgstattuple('pg_catalog.pg_proc');
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-[ RECORD 1 ]------+-------
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table_len | 458752
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tuple_count | 1470
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tuple_len | 438896
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tuple_percent | 95.67
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dead_tuple_count | 11
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dead_tuple_len | 3157
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dead_tuple_percent | 0.69
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free_space | 8932
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free_percent | 1.95
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</programlisting>
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<para>
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The output columns are:
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</para>
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<table>
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<title><function>pgstattuple</function> output columns</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>Column</entry>
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<entry>Type</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><structfield>table_len</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Physical relation length in bytes</entry>
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</row>
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<row>
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<entry><structfield>tuple_count</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Number of live tuples</entry>
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</row>
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<row>
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<entry><structfield>tuple_len</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Total length of live tuples in bytes</entry>
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</row>
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<row>
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<entry><structfield>tuple_percent</structfield></entry>
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<entry><type>float8</type></entry>
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<entry>Percentage of live tuples</entry>
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</row>
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<row>
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<entry><structfield>dead_tuple_count</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Number of dead tuples</entry>
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</row>
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<row>
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<entry><structfield>dead_tuple_len</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Total length of dead tuples in bytes</entry>
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</row>
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<row>
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<entry><structfield>dead_tuple_percent</structfield></entry>
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<entry><type>float8</type></entry>
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<entry>Percentage of dead tuples</entry>
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</row>
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<row>
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<entry><structfield>free_space</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Total free space in bytes</entry>
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</row>
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<row>
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<entry><structfield>free_percent</structfield></entry>
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<entry><type>float8</type></entry>
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<entry>Percentage of free space</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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<para>
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<function>pgstattuple</function> acquires only a read lock on the
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relation. So the results do not reflect an instantaneous snapshot;
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concurrent updates will affect them.
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</para>
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<para>
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<function>pgstattuple</function> judges a tuple is <quote>dead</> if
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<function>HeapTupleSatisfiesNow</> returns false.
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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>pgstattuple(oid) returns record</>
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</term>
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<listitem>
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<para>
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This is the same as <function>pgstattuple(text)</function>, except
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that the target relation is specified by OID.
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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>pgstatindex(text) returns record</>
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</term>
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<listitem>
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<para>
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<function>pgstatindex</function> returns a record showing information
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about a btree index. For example:
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</para>
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<programlisting>
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test=> SELECT * FROM pgstatindex('pg_cast_oid_index');
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-[ RECORD 1 ]------+------
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version | 2
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tree_level | 0
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index_size | 8192
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root_block_no | 1
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internal_pages | 0
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leaf_pages | 1
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empty_pages | 0
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deleted_pages | 0
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avg_leaf_density | 50.27
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leaf_fragmentation | 0
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</programlisting>
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<para>
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The output columns are:
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</para>
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<table>
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<title><function>pgstatindex</function> output columns</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>Column</entry>
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<entry>Type</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><structfield>version</structfield></entry>
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<entry><type>integer</type></entry>
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<entry>Btree version number</entry>
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</row>
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<row>
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<entry><structfield>tree_level</structfield></entry>
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<entry><type>integer</type></entry>
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<entry>Tree level of the root page</entry>
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</row>
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<row>
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<entry><structfield>index_size</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Total number of pages in index</entry>
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</row>
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<row>
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<entry><structfield>root_block_no</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Location of root block</entry>
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</row>
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<row>
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<entry><structfield>internal_pages</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Number of <quote>internal</> (upper-level) pages</entry>
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</row>
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<row>
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<entry><structfield>leaf_pages</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Number of leaf pages</entry>
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</row>
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<row>
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<entry><structfield>empty_pages</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Number of empty pages</entry>
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</row>
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<row>
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<entry><structfield>deleted_pages</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry>Number of deleted pages</entry>
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</row>
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<row>
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<entry><structfield>avg_leaf_density</structfield></entry>
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<entry><type>float8</type></entry>
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<entry>Average density of leaf pages</entry>
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</row>
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<row>
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<entry><structfield>leaf_fragmentation</structfield></entry>
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<entry><type>float8</type></entry>
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<entry>Leaf page fragmentation</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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<para>
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As with <function>pgstattuple</>, the results are accumulated
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page-by-page, and should not be expected to represent an
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instantaneous snapshot of the whole index.
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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>pg_relpages(text) returns bigint</>
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</term>
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<listitem>
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<para>
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<function>pg_relpages</function> returns the number of pages in the
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relation.
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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>
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<title>Authors</title>
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<para>
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Tatsuo Ishii and Satoshi Nagayasu
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</para>
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</sect2>
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</sect1>
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