<sect2 id="functions-info-wal-summary">

<title>WAL Summarization Information Functions</title>

<para>

The functions shown in <xref linkend="functions-wal-summary"/>

print information about the status of WAL summarization.

See <xref linkend="guc-summarize-wal" />.

</para>

<table id="functions-wal-summary">

<title>WAL Summarization Information Functions</title>

<tgroup cols="1">

<thead>

<row>

<entry role="func_table_entry"><para role="func_signature">

Function

</para>

<para>

Description

</para></entry>

</row>

</thead>

<tbody>

<row>

<entry role="func_table_entry"><para role="func_signature">

<indexterm>

<primary>pg_available_wal_summaries</primary>

</indexterm>

<function>pg_available_wal_summaries</function> ()

<returnvalue>setof record</returnvalue>

( <parameter>tli</parameter> <type>bigint</type>,

<parameter>start_lsn</parameter> <type>pg_lsn</type>,

<parameter>end_lsn</parameter> <type>pg_lsn</type> )

</para>

<para>

Returns information about the WAL summary files present in the

data directory, under <literal>pg_wal/summaries</literal>.

One row will be returned per WAL summary file. Each file summarizes

WAL on the indicated TLI within the indicated LSN range. This function

might be useful to determine whether enough WAL summaries are present

on the server to take an incremental backup based on some prior

backup whose start LSN is known.

</para></entry>

</row>

<row>

<entry role="func_table_entry"><para role="func_signature">

<indexterm>

<primary>pg_wal_summary_contents</primary>

</indexterm>

<function>pg_wal_summary_contents</function> ( <parameter>tli</parameter> <type>bigint</type>, <parameter>start_lsn</parameter> <type>pg_lsn</type>, <parameter>end_lsn</parameter> <type>pg_lsn</type> )

<returnvalue>setof record</returnvalue>

( <parameter>relfilenode</parameter> <type>oid</type>,

<parameter>reltablespace</parameter> <type>oid</type>,

<parameter>reldatabase</parameter> <type>oid</type>,

<parameter>relforknumber</parameter> <type>smallint</type>,

<parameter>relblocknumber</parameter> <type>bigint</type>,

<parameter>is_limit_block</parameter> <type>boolean</type> )

</para>

<para>

Returns one information about the contents of a single WAL summary file

identified by TLI and starting and ending LSNs. Each row with

<literal>is_limit_block</literal> false indicates that the block

identified by the remaining output columns was modified by at least

one WAL record within the range of records summarized by this file.

Each row with <literal>is_limit_block</literal> true indicates either

that (a) the relation fork was truncated to the length given by

<literal>relblocknumber</literal> within the relevant range of WAL

records or (b) that the relation fork was created or dropped within

the relevant range of WAL records; in such cases,

<literal>relblocknumber</literal> will be zero.

</para></entry>

</row>

</tbody>

</tgroup>

</table>

</sect2>