On Tue, Jun 9, 2015 at 05:20:23PM -0700, Jeff Janes wrote: > On Tue, Jun 9, 2015 at 4:20 PM, Thomas Munro <thomas.mu...@enterprisedb.com> > wrote: > > Hi > > Why do standby servers not simply treat every checkpoint as a > restartpoint? As I understand it, setting checkpoint_timeout and > checkpoint_segments higher on a standby server effectively instruct > standby servers to skip some checkpoints. Even with the same settings > on both servers, the server could still choose to skip a checkpoint > near the checkpoint_timeout limit due to the vagaries of time keeping > (though I suppose it's very unlikely). But what could the advantage > of skipping checkpoints be? Do people deliberately set hot standby > machines up like this to trade a longer crash recover time for lower > write IO? > > > When a hot standby server is initially being set up using a rather old base > backup and an archive directory, it could be applying WAL at a very high rate > such that it would replay master checkpoints multiple times a second (when the > master has long periods with little write activity and has checkpoints driven > by timeouts during those periods). Actually doing restartpoints that often > could be annoying. Presumably there would be few dirty buffers to write out, > since each checkpoint saw little activity, but you would still have to circle > the shared_buffers twice, and fsync whichever files did happen to get some > changes.
Ah, so even thought standbys don't have to write WAL, they are fsyncing shared buffers. Where is the restart point recorded, in pg_controldata? c -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
