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Implement backup API functions for non-exclusive backups

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Previously non-exclusive backups had to be done using the replication protocol
and pg_basebackup. With this commit it's now possible to make them using
pg_start_backup/pg_stop_backup as well, as long as the backup program can
maintain a persistent connection to the database.

Doing this, backup_label and tablespace_map are returned as results from
pg_stop_backup() instead of being written to the data directory. This makes
the server safe from a crash during an ongoing backup, which can be a problem
with exclusive backups.

The old syntax of the functions remain and work exactly as before, but since the
new syntax is safer this should eventually be deprecated and removed.

Only reference documentation is included. The main section on backup still needs
to be rewritten to cover this, but since that is already scheduled for a separate
large rewrite, it's not included in this patch.

Reviewed by David Steele and Amit Kapila
This commit is contained in:
Magnus Hagander
2016-04-05 20:03:49 +02:00
parent 9457b591b9
commit 7117685461
9 changed files with 265 additions and 53 deletions
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48
doc/src/sgml/func.sgml
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@ -17478,7 +17478,7 @@ SELECT set_config('log_statement_stats', 'off', false);
</row>
<row>
<entry>
<literal><function>pg_start_backup(<parameter>label</> <type>text</> <optional>, <parameter>fast</> <type>boolean</> </optional>)</function></literal>
<literal><function>pg_start_backup(<parameter>label</> <type>text</> <optional>, <parameter>fast</> <type>boolean</> <optional>, <parameter>exclusive</> <type>boolean</> </optional></optional>)</function></literal>
</entry>
<entry><type>pg_lsn</type></entry>
<entry>Prepare for performing on-line backup (restricted to superusers or replication roles)</entry>
@ -17488,7 +17488,14 @@ SELECT set_config('log_statement_stats', 'off', false);
<literal><function>pg_stop_backup()</function></literal>
</entry>
<entry><type>pg_lsn</type></entry>
<entry>Finish performing on-line backup (restricted to superusers or replication roles)</entry>
<entry>Finish performing exclusive on-line backup (restricted to superusers or replication roles)</entry>
</row>
<row>
<entry>
<literal><function>pg_stop_backup(<parameter>exclusive</> <type>boolean</>)</function></literal>
</entry>
<entry><type>setof record</type></entry>
<entry>Finish performing exclusive or non-exclusive on-line backup (restricted to superusers or replication roles)</entry>
</row>
<row>
<entry>
@ -17537,15 +17544,19 @@ SELECT set_config('log_statement_stats', 'off', false);
</table>
<para>
<function>pg_start_backup</> accepts 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 (<filename>backup_label</>) and, if there
are any links in the <filename>pg_tblspc/</> directory, a tablespace map
file (<filename>tablespace_map</>) into the database cluster's data
directory, performs a checkpoint, and then returns the backup's starting
transaction log location as text. The user can ignore this result value,
but it is provided in case it is useful.
<function>pg_start_backup</> accepts an arbitrary user-defined label for
the backup. (Typically this would be the name under which the backup dump
file will be stored.) When used in exclusive mode, the function writes a
backup label file (<filename>backup_label</>) and, if there are any links
in the <filename>pg_tblspc/</> directory, a tablespace map file
(<filename>tablespace_map</>) into the database cluster's data directory,
performs a checkpoint, and then returns the backup's starting transaction
log location as text. The user can ignore this result value, but it is
provided in case it is useful. When used in non-exclusive mode, the
contents of these files are instead returned by the
<function>pg_stop_backup</> function, and should be written to the backup
by the caller.
<programlisting>
postgres=# select pg_start_backup('label_goes_here');
pg_start_backup
@ -17560,10 +17571,17 @@ postgres=# select pg_start_backup('label_goes_here');
</para>
<para>
<function>pg_stop_backup</> removes the label file and, if it exists,
the <filename>tablespace_map</> file created by
<function>pg_start_backup</>, and creates a backup history file in
the transaction log archive area. The history file includes the label given to
In an exclusive backup, <function>pg_stop_backup</> removes the label file
and, if it exists, the <filename>tablespace_map</> file created by
<function>pg_start_backup</>. In a non-exclusive backup, the contents of
the <filename>backup_label</> and <filename>tablespace_map</> are returned
in the result of the function, and should be written to files in the
backup (and not in the data directory).
</para>
<para>
The function also creates a backup history file in the transaction log
archive area. The history file includes the label given to
<function>pg_start_backup</>, the starting and ending transaction log locations for
the backup, and the starting and ending times of the backup. The return
value is the backup's ending transaction log location (which again