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Expose control file data via SQL accessible functions.
Add four new SQL accessible functions: pg_control_system(), pg_control_checkpoint(), pg_control_recovery(), and pg_control_init() which expose a subset of the control file data. Along the way move the code to read and validate the control file to src/common, where it can be shared by the new backend functions and the original pg_controldata frontend program. Patch by me, significant input, testing, and review by Michael Paquier.
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‎doc/src/sgml/func.sgml‎

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@@ -16703,6 +16703,362 @@ SELECT collation for ('foo' COLLATE "de_DE");
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</tgroup>
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</table>
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<para>
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The functions shown in <xref linkend="functions-controldata">
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print information initialized during <command>initdb</>, such
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as the catalog version. They also show information about write-ahead
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logging and checkpoint processing. This information is cluster-wide,
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and not specific to any one database. They provide most of the same
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information, from the same source, as
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<xref linkend="APP-PGCONTROLDATA">, although in a form better suited
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to <acronym>SQL</acronym> functions.
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</para>
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<table id="functions-controldata">
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<title>Control Data Functions</title>
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<tgroup cols="3">
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<thead>
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<row><entry>Name</entry> <entry>Return Type</entry> <entry>Description</entry></row>
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</thead>
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<tbody>
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<row>
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<entry>
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<indexterm><primary>pg_control_checkpoint</primary></indexterm>
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<literal><function>pg_control_checkpoint()</function></literal>
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</entry>
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<entry><type>record</type></entry>
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<entry>
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Returns information about current checkpoint state.
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</entry>
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</row>
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<row>
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<entry>
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<indexterm><primary>pg_control_system</primary></indexterm>
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<literal><function>pg_control_system()</function></literal>
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</entry>
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<entry><type>record</type></entry>
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<entry>
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Returns information about current controldata file state.
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</entry>
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</row>
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<row>
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<entry>
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<indexterm><primary>pg_control_init</primary></indexterm>
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<literal><function>pg_control_init()</function></literal>
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</entry>
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<entry><type>record</type></entry>
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<entry>
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Returns information about cluster initialization state.
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</entry>
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</row>
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<row>
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<entry>
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<indexterm><primary>pg_control_recovery</primary></indexterm>
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<literal><function>pg_control_recovery()</function></literal>
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</entry>
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<entry><type>record</type></entry>
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<entry>
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Returns information about recovery state.
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</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>pg_control_checkpoint</> returns a record, shown in
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<xref linkend="functions-pg-control-checkpoint">
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</para>
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<table id="functions-pg-control-checkpoint">
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<title><function>pg_control_checkpoint</> Columns</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Column Name</entry>
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<entry>Data Type</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>checkpoint_location</entry>
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<entry><type>pg_lsn</type></entry>
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</row>
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<row>
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<entry>prior_location</entry>
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<entry><type>pg_lsn</type></entry>
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</row>
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<row>
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<entry>redo_location</entry>
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<entry><type>pg_lsn</type></entry>
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</row>
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<row>
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<entry>redo_wal_file</entry>
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<entry><type>text</type></entry>
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</row>
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<row>
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<entry>timeline_id</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>prev_timeline_id</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>full_page_writes</entry>
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<entry><type>boolean</type></entry>
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</row>
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<row>
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<entry>next_xid</entry>
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<entry><type>text</type></entry>
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</row>
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<row>
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<entry>next_oid</entry>
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<entry><type>oid</type></entry>
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</row>
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<row>
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<entry>next_multixact_id</entry>
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<entry><type>xid</type></entry>
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</row>
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<row>
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<entry>next_multi_offset</entry>
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<entry><type>xid</type></entry>
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</row>
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<row>
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<entry>oldest_xid</entry>
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<entry><type>xid</type></entry>
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</row>
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<row>
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<entry>oldest_xid_dbid</entry>
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<entry><type>oid</type></entry>
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</row>
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<row>
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<entry>oldest_active_xid</entry>
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<entry><type>xid</type></entry>
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</row>
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<row>
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<entry>oldest_multi_xid</entry>
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<entry><type>xid</type></entry>
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</row>
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<row>
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<entry>oldest_multi_dbid</entry>
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<entry><type>oid</type></entry>
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</row>
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<row>
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<entry>oldest_commit_ts_xid</entry>
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<entry><type>xid</type></entry>
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</row>
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<row>
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<entry>newest_commit_ts_xid</entry>
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<entry><type>xid</type></entry>
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</row>
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<row>
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<entry>checkpoint_time</entry>
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<entry><type>timestamp with time zone</type></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>pg_control_system</> returns a record, shown in
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<xref linkend="functions-pg-control-system">
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</para>
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<table id="functions-pg-control-system">
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<title><function>pg_control_system</> Columns</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Column Name</entry>
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<entry>Data Type</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>pg_control_version</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>catalog_version_no</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>system_identifier</entry>
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<entry><type>bigint</type></entry>
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</row>
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<row>
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<entry>pg_control_last_modified</entry>
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<entry><type>timestamp with time zone</type></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>pg_control_init</> returns a record, shown in
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<xref linkend="functions-pg-control-init">
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</para>
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<table id="functions-pg-control-init">
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<title><function>pg_control_init</> Columns</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Column Name</entry>
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<entry>Data Type</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>max_data_alignment</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>database_block_size</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>blocks_per_segment</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>wal_block_size</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>bytes_per_wal_segment</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>max_identifier_length</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>max_index_columns</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>max_toast_chunk_size</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>large_object_chunk_size</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>bigint_timestamps</entry>
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<entry><type>boolean</type></entry>
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</row>
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<row>
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<entry>float4_pass_by_value</entry>
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<entry><type>boolean</type></entry>
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</row>
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<row>
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<entry>float8_pass_by_value</entry>
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<entry><type>boolean</type></entry>
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</row>
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<row>
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<entry>data_page_checksum_version</entry>
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<entry><type>integer</type></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>pg_control_recovery</> returns a record, shown in
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<xref linkend="functions-pg-control-recovery">
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</para>
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<table id="functions-pg-control-recovery">
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<title><function>pg_control_recovery</> Columns</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Column Name</entry>
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<entry>Data Type</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>min_recovery_end_location</entry>
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<entry><type>pg_lsn</type></entry>
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</row>
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<row>
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<entry>min_recovery_end_timeline</entry>
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry>backup_start_location</entry>
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<entry><type>pg_lsn</type></entry>
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</row>
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<row>
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<entry>backup_end_location</entry>
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<entry><type>pg_lsn</type></entry>
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</row>
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<row>
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<entry>end_of_backup_record_required</entry>
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<entry><type>boolean</type></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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</sect1>
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<sect1 id="functions-admin">

‎src/backend/utils/misc/Makefile‎

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override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS)
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17-
OBJS = guc.o help_config.o pg_config.o pg_rusage.o \
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OBJS = guc.o help_config.o pg_config.o pg_controldata.o pg_rusage.o \
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ps_status.o rls.o sampling.o superuser.o timeout.o tzparser.o
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2020
# This location might depend on the installation directories. Therefore

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