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pg_dump: Support using synchronized snapshots on standbys 

This became possible by commit
6c2003f8a1.  This just makes pg_dump aware
of it and updates the documentation.

Author: Petr Jelinek <petr.jelinek@2ndquadrant.com>
This commit is contained in:
Peter Eisentraut 2017-08-16 19:46:50 -04:00
parent dcd052c8d2
commit cf851519d4
2 changed files with 12 additions and 10 deletions
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18
doc/src/sgml/ref/pg_dump.sgml
View File

@ -337,14 +337,16 @@ PostgreSQL documentation
but to abort the dump.
</para>
<para>
For a consistent backup, the database server needs to support synchronized snapshots,
a feature that was introduced in <productname>PostgreSQL</productname> 9.2. With this
feature, database clients can ensure they see the same data set even though they use
different connections. <command>pg_dump -j</command> uses multiple database
connections; it connects to the database once with the master process and
once again for each worker job. Without the synchronized snapshot feature, the
different worker jobs wouldn't be guaranteed to see the same data in each connection,
which could lead to an inconsistent backup.
For a consistent backup, the database server needs to support
synchronized snapshots, a feature that was introduced in
<productname>PostgreSQL</productname> 9.2 for primary servers and 10
for standbys. With this feature, database clients can ensure they see
the same data set even though they use different connections.
<command>pg_dump -j</command> uses multiple database connections; it
connects to the database once with the master process and once again
for each worker job. Without the synchronized snapshot feature, the
different worker jobs wouldn't be guaranteed to see the same data in
each connection, which could lead to an inconsistent backup.
</para>
<para>
If you want to run a parallel dump of a pre-9.2 server, you need to make sure that the

4
src/bin/pg_dump/pg_dump.c
View File

@ -1134,9 +1134,9 @@ setup_connection(Archive *AH, const char *dumpencoding,
AH->remoteVersion >= 90200 &&
!dopt->no_synchronized_snapshots)
{
if (AH->isStandby)
if (AH->isStandby && AH->remoteVersion < 100000)
exit_horribly(NULL,
"Synchronized snapshots are not supported on standby servers.\n"
"Synchronized snapshots on standby servers are not supported by this server version.\n"
"Run with --no-synchronized-snapshots instead if you do not need\n"
"synchronized snapshots.\n");