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Add an optional parameter to pg_start_backup() that specifies whether to do

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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
2009-04-07 00:31:26 +00:00
parent 80df9c49af
commit 387060951e
6 changed files with 54 additions and 27 deletions
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21
doc/src/sgml/func.sgml
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@@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.474 2009/04/01 03:32:29 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.475 2009/04/07 00:31:25 tgl Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@@ -12880,10 +12880,10 @@ SELECT set_config('log_statement_stats', 'off', false);
<tbody>
<row>
<entry>
<literal><function>pg_start_backup</function>(<parameter>label</> <type>text</>)</literal>
<literal><function>pg_start_backup</function>(<parameter>label</> <type>text</> <optional>, <parameter>fast</> <type>boolean</> </optional>)</literal>
</entry>
<entry><type>text</type></entry>
<entry>Set up for performing on-line backup</entry>
<entry>Prepare for performing on-line backup</entry>
</row>
<row>
<entry>
@@ -12932,13 +12932,14 @@ SELECT set_config('log_statement_stats', 'off', false);
</table>
<para>
<function>pg_start_backup</> accepts a single parameter which is an
<function>pg_start_backup</> accepts a text parameter which is an
arbitrary user-defined label for the backup. (Typically this would be
the name under which the backup dump file will be stored.) The function
writes a backup label file into the database cluster's data directory,
and then returns the backup's starting transaction log location as text. The user
need not pay any attention to this result value, but it is provided in
case it is of use.
performs a checkpoint,
and then returns the backup's starting transaction log location as text.
The user need not pay any attention to this result value, but it is
provided in case it is of use.
<programlisting>
postgres=# select pg_start_backup('label_goes_here');
pg_start_backup
@@ -12946,6 +12947,10 @@ postgres=# select pg_start_backup('label_goes_here');
0/D4445B8
(1 row)
</programlisting>
There is an optional boolean second parameter. If <literal>true</>,
it specifies executing <function>pg_start_backup</> as quickly as
possible. This forces an immediate checkpoint which will cause a
spike in I/O operations, slowing any concurrently executing queries.
</para>
<para>
@@ -12961,7 +12966,7 @@ postgres=# select pg_start_backup('label_goes_here');
</para>
<para>
<function>pg_switch_xlog</> moves to the next transaction log file, allowing the
<function>pg_switch_xlog</> moves to the next transaction log file, allowing the
current file to be archived (assuming you are using continuous archiving).
The result is the ending transaction log location + 1 within the just-completed transaction log file.
If there has been no transaction log activity since the last transaction log switch,