diff options
| author | Andres Freund | 2017-06-14 18:57:21 +0000 |
|---|---|---|
| committer | Andres Freund | 2017-06-14 18:57:21 +0000 |
| commit | 6c2003f8a1bbc7c192a2e83ec51581c018aa162f (patch) | |
| tree | ba5318272f4c1995f736d0367315432bafeaa41f /doc/src | |
| parent | b6966d4627c0297ad42fe2592c66ac2f76e9962e (diff) | |
Don't force-assign transaction id when exporting a snapshot.
Previously we required every exported transaction to have an xid
assigned. That was used to check that the exporting transaction is
still running, which in turn is needed to guarantee that that
necessary rows haven't been removed in between exporting and importing
the snapshot.
The exported xid caused unnecessary problems with logical decoding,
because slot creation has to wait for all concurrent xid to finish,
which in turn serializes concurrent slot creation. It also
prohibited snapshots to be exported on hot-standby replicas.
Instead export the virtual transactionid, which avoids the unnecessary
serialization and the inability to export snapshots on standbys. This
changes the file name of the exported snapshot, but since we never
documented what that one means, that seems ok.
Author: Petr Jelinek, slightly editorialized by me
Reviewed-By: Andres Freund
Discussion: https://postgr.es/m/f598b4b8-8cd7-0d54-0939-adda763d8c34@2ndquadrant.com
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/ref/set_transaction.sgml | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/doc/src/sgml/ref/set_transaction.sgml b/doc/src/sgml/ref/set_transaction.sgml index ca55a5b196..188d2ed92e 100644 --- a/doc/src/sgml/ref/set_transaction.sgml +++ b/doc/src/sgml/ref/set_transaction.sgml @@ -222,8 +222,8 @@ SET SESSION CHARACTERISTICS AS TRANSACTION <replaceable class="parameter">transa BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ; SELECT pg_export_snapshot(); pg_export_snapshot --------------------- - 000003A1-1 +--------------------- + 00000003-0000001B-1 (1 row) </programlisting> @@ -233,7 +233,7 @@ SELECT pg_export_snapshot(); <programlisting> BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ; -SET TRANSACTION SNAPSHOT '000003A1-1'; +SET TRANSACTION SNAPSHOT '00000003-0000001B-1'; </programlisting></para> </refsect1> |