Streaming Replication: Checkpoint_segment and wal_keep_segments on standby
in [PgSql]
|
Prev: [HACKERS] Streaming Replication: Checkpoint_segment and wal_keep_segments on standby
Next: [HACKERS] 9.0beta2 release plans
From: Fujii Masao on 1 Jul 2010 00:09 On Thu, Jul 1, 2010 at 11:39 AM, Bruce Momjian <bruce(a)momjian.us> wrote: > > Did these changes ever get into the docs? I don't think so. Thanks for reminding me. I attached the updated patch. > > That last sentence is a bit unclear. How about: > > > > A restartpoint is triggered if at least one checkpoint record has been > > replayed and <varname>checkpoint_timeout</> seconds have passed since last > > restartpoint. In standby mode, a restartpoint is also triggered if > > <varname>checkoint_segments</> log segments have been replayed since last > > restartpoint and at least one checkpoint record has been replayed since. > >> ... In log shipping case, the checkpoint interval > >> + ? ?on the standby is normally smaller than that on the master. > >> + ? </para> > > > > What does that mean? Restartpoints can't be performed more frequently than > > checkpoints in the master because restartpoints can only be performed at > > checkpoint records. I adopted these Heikki's sentences. > >> *** a/doc/src/sgml/wal.sgml > >> --- b/doc/src/sgml/wal.sgml > >> *************** > >> *** 424,429 **** > >> --- 424,430 ---- > >> ? ?<para> > >> ? ? There will always be at least one WAL segment file, and will normally > >> ? ? not be more than (2 + <varname>checkpoint_completion_target</varname>) > >> * <varname>checkpoint_segments</varname> + 1 > >> + ? ?or <varname>checkpoint_segments</> + <xref > >> linkend="guc-wal-keep-segments"> + 1 > >> ? ? files. ?Each segment file is normally 16 MB (though this size can be > >> ? ? altered when building the server). ?You can use this to estimate space > >> ? ? requirements for <acronym>WAL</acronym>. > > > > That's not true, wal_keep_segments is the minimum number of files retained, > > independently of checkpoint_segments. The corret formula is (2 + > > checkpoint_completion_target * checkpoint_segments, wal_keep_segments) > > You mean that the maximum number of WAL files is: ? > > max { > (2 + checkpoint_completion_target) * checkpoint_segments, > wal_keep_segments > } > > Just after a checkpoint removes old WAL files, there might be wal_keep_segments > WAL files. Additionally, checkpoint_segments WAL files might be generated before > the subsequent checkpoint removes old WAL files. So I think that the maximum > number is > > max { > (2 + checkpoint_completion_target) * checkpoint_segments, > wal_keep_segments + checkpoint_segments > } > > Am I missing something? I've left this part as it is. Before committing the patch, we need to check whether my thought is true. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center
From: Fujii Masao on 16 Jul 2010 04:13
On Thu, Jul 1, 2010 at 1:09 PM, Fujii Masao <masao.fujii(a)gmail.com> wrote: > Thanks for reminding me. I attached the updated patch. This patch left uncommitted for half a month. No one is interested in the patch? The patch adds the document about the relationship between a restartpoint and checkpoint_segments parameter. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers |