Add an optional parameter to pg_start_backup() that specifies whether to do
the checkpoint in immediate or lazy mode. This is to address complaints that pg_start_backup() takes a long time even when there's no need to minimize its I/O consumption.
This commit is contained in:
Tom Lane
parent
80df9c49af
commit
387060951e
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.123 2009/03/05 19:50:03 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.124 2009/04/07 00:31:25 tgl Exp $ -->
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<chapter id="backup">
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<title>Backup and Restore</title>
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@ -730,19 +730,19 @@ SELECT pg_start_backup('label');
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</para>
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<para>
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<function>pg_start_backup</> can take a long time to finish.
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By default, <function>pg_start_backup</> can take a long time to finish.
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This is because it performs a checkpoint, and the I/O
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required for a checkpoint will be spread out over a significant
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required for the checkpoint will be spread out over a significant
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period of time, by default half your inter-checkpoint interval
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(see the configuration parameter
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<xref linkend="guc-checkpoint-completion-target">). Usually
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this is what you want because it minimizes the impact on query
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this is what you want, because it minimizes the impact on query
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processing. If you just want to start the backup as soon as
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possible, execute a <command>CHECKPOINT</> command
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(which performs a checkpoint as quickly as possible) and then
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immediately execute <function>pg_start_backup</>. Then there
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will be very little for <function>pg_start_backup</>'s checkpoint
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to do, and it won't take long.
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possible, use:
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<programlisting>
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SELECT pg_start_backup('label', true);
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</programlisting>
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This forces the checkpoint to be done as quickly as possible.
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</para>
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</listitem>
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<listitem>
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@ -769,9 +769,9 @@ SELECT pg_stop_backup();
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<para>
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Once the WAL segment files used during the backup are archived, you are
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done. The file identified by <function>pg_stop_backup</>'s result is
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the last segment that is required to form a complete set of backup files.
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the last segment that is required to form a complete set of backup files.
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<function>pg_stop_backup</> does not return until the last segment has
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been archived.
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been archived.
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Archiving of these files happens automatically since you have
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already configured <varname>archive_command</>. In most cases this
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happens quickly, but you are advised to monitor your archive
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.474 2009/04/01 03:32:29 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.475 2009/04/07 00:31:25 tgl Exp $ -->
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<chapter id="functions">
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<title>Functions and Operators</title>
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@ -12880,10 +12880,10 @@ SELECT set_config('log_statement_stats', 'off', false);
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<tbody>
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<row>
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<entry>
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<literal><function>pg_start_backup</function>(<parameter>label</> <type>text</>)</literal>
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<literal><function>pg_start_backup</function>(<parameter>label</> <type>text</> <optional>, <parameter>fast</> <type>boolean</> </optional>)</literal>
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</entry>
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<entry><type>text</type></entry>
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<entry>Set up for performing on-line backup</entry>
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<entry>Prepare for performing on-line backup</entry>
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</row>
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<row>
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<entry>
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@ -12932,13 +12932,14 @@ SELECT set_config('log_statement_stats', 'off', false);
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</table>
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<para>
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<function>pg_start_backup</> accepts a single parameter which is an
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<function>pg_start_backup</> accepts a text parameter which is an
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arbitrary user-defined label for the backup. (Typically this would be
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the name under which the backup dump file will be stored.) The function
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writes a backup label file into the database cluster's data directory,
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and then returns the backup's starting transaction log location as text. The user
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need not pay any attention to this result value, but it is provided in
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case it is of use.
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performs a checkpoint,
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and then returns the backup's starting transaction log location as text.
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The user need not pay any attention to this result value, but it is
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provided in case it is of use.
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<programlisting>
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postgres=# select pg_start_backup('label_goes_here');
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pg_start_backup
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@ -12946,6 +12947,10 @@ postgres=# select pg_start_backup('label_goes_here');
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0/D4445B8
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(1 row)
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</programlisting>
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There is an optional boolean second parameter. If <literal>true</>,
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it specifies executing <function>pg_start_backup</> as quickly as
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possible. This forces an immediate checkpoint which will cause a
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spike in I/O operations, slowing any concurrently executing queries.
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</para>
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<para>
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@ -12961,7 +12966,7 @@ postgres=# select pg_start_backup('label_goes_here');
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</para>
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<para>
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<function>pg_switch_xlog</> moves to the next transaction log file, allowing the
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<function>pg_switch_xlog</> moves to the next transaction log file, allowing the
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current file to be archived (assuming you are using continuous archiving).
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The result is the ending transaction log location + 1 within the just-completed transaction log file.
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If there has been no transaction log activity since the last transaction log switch,
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@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.334 2009/03/11 23:19:24 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.335 2009/04/07 00:31:26 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -6914,6 +6914,7 @@ Datum
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pg_start_backup(PG_FUNCTION_ARGS)
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{
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text *backupid = PG_GETARG_TEXT_P(0);
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bool fast = PG_GETARG_BOOL(1);
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char *backupidstr;
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XLogRecPtr checkpointloc;
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XLogRecPtr startpoint;
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@ -6983,9 +6984,11 @@ pg_start_backup(PG_FUNCTION_ARGS)
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* have different checkpoint positions and hence different history
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* file names, even if nothing happened in between.
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*
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* We don't use CHECKPOINT_IMMEDIATE, hence this can take awhile.
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* We use CHECKPOINT_IMMEDIATE only if requested by user (via
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* passing fast = true). Otherwise this can take awhile.
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*/
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RequestCheckpoint(CHECKPOINT_FORCE | CHECKPOINT_WAIT);
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RequestCheckpoint(CHECKPOINT_FORCE | CHECKPOINT_WAIT |
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(fast ? CHECKPOINT_IMMEDIATE : 0));
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/*
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* Now we need to fetch the checkpoint record location, and also its
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@ -3,7 +3,7 @@
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*
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* Copyright (c) 1996-2009, PostgreSQL Global Development Group
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*
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* $PostgreSQL: pgsql/src/backend/catalog/system_views.sql,v 1.59 2009/02/06 21:15:11 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/catalog/system_views.sql,v 1.60 2009/04/07 00:31:26 tgl Exp $
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*/
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CREATE VIEW pg_roles AS
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@ -403,6 +403,12 @@ CREATE VIEW pg_user_mappings AS
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REVOKE ALL on pg_user_mapping FROM public;
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--
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-- We have a few function definitions in here, too.
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-- At some point there might be enough to justify breaking them out into
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-- a separate "system_functions.sql" file.
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--
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-- Tsearch debug function. Defined here because it'd be pretty unwieldy
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-- to put it into pg_proc.h
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@ -464,3 +470,16 @@ LANGUAGE SQL STRICT STABLE;
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COMMENT ON FUNCTION ts_debug(text) IS
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'debug function for current text search configuration';
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--
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-- Redeclare built-in functions that need default values attached to their
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-- arguments. It's impractical to set those up directly in pg_proc.h because
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-- of the complexity and platform-dependency of the expression tree
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-- representation. (Note that internal functions still have to have entries
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-- in pg_proc.h; we are merely causing their proargnames and proargdefaults
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-- to get filled in.)
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--
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CREATE OR REPLACE FUNCTION
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pg_start_backup(label text, fast boolean DEFAULT false)
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RETURNS text STRICT VOLATILE LANGUAGE internal AS 'pg_start_backup';
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@ -37,7 +37,7 @@
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* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.528 2009/04/05 22:28:59 tgl Exp $
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* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.529 2009/04/07 00:31:26 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -53,6 +53,6 @@
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*/
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/* yyyymmddN */
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#define CATALOG_VERSION_NO 200904051
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#define CATALOG_VERSION_NO 200904061
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#endif
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@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.540 2009/04/05 22:28:59 tgl Exp $
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* $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.541 2009/04/07 00:31:26 tgl Exp $
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*
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* NOTES
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* The script catalog/genbki.sh reads this file and generates .bki
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@ -3252,7 +3252,7 @@ DATA(insert OID = 2171 ( pg_cancel_backend PGNSP PGUID 12 1 0 0 f f f t f v 1 0
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DESCR("cancel a server process' current query");
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DATA(insert OID = 2096 ( pg_terminate_backend PGNSP PGUID 12 1 0 0 f f f t f v 1 0 16 "23" _null_ _null_ _null_ _null_ pg_terminate_backend _null_ _null_ _null_ ));
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DESCR("terminate a server process");
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DATA(insert OID = 2172 ( pg_start_backup PGNSP PGUID 12 1 0 0 f f f t f v 1 0 25 "25" _null_ _null_ _null_ _null_ pg_start_backup _null_ _null_ _null_ ));
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DATA(insert OID = 2172 ( pg_start_backup PGNSP PGUID 12 1 0 0 f f f t f v 2 0 25 "25 16" _null_ _null_ _null_ _null_ pg_start_backup _null_ _null_ _null_ ));
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DESCR("prepare for taking an online backup");
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DATA(insert OID = 2173 ( pg_stop_backup PGNSP PGUID 12 1 0 0 f f f t f v 0 0 25 "" _null_ _null_ _null_ _null_ pg_stop_backup _null_ _null_ _null_ ));
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DESCR("finish taking an online backup");
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