On Fri, Jul 27, 2012 at 02:13:31PM +1000, Chris Angelico wrote: > On Fri, Jul 27, 2012 at 9:57 AM, Chris Angelico <rosuav@xxxxxxxxx> wrote: > > On Fri, Jul 27, 2012 at 9:53 AM, Bruce Momjian <bruce@xxxxxxxxxx> wrote: > >> You might want to look at the hackers list thread I started about the > >> same topic a week before your post: > >> > >> http://archives.postgresql.org/pgsql-hackers/2012-07/msg00416.php > >> > >> Basically, you can only use mtime/size if you are replaying WAL. > > > > I'll check that out in a bit; but hot standby includes replaying WAL, > > right? That's what we're doing - full live replication with > > possibility to "pg_ctl promote" a slave straight up to master. > > Hi, thanks for that link. Just got a chance to read through the thread. > > In this post[1] the script executes "checkpoint" before > "pg_start_backup" - is that important? According to the docs[2]: > > "There is an optional second parameter of type boolean. If true, it > specifies executing pg_start_backup as quickly as possible. This > forces an immediate checkpoint which will cause a spike in I/O > operations, slowing any concurrently executing queries." A checkpoint is always issued by pg_start_backup(). The boolean controls whether the checkpoint is immediate or smoothed, meaning it can take a while to return a status of complete. > Is "checkpoint; select pg_start_backup('foo');" the same as "select > pg_start_backup('foo',true);"? And what are the consequences of not > calling for a checkpoint that way? My understanding of the docs is > that the pg_start_backup call will hang until a checkpoint happens > organically, ie delaying the backup rather than other clients, but I'm > not really sure and haven't a sample database big or busy enough to > test this on. Right, checkpoint is started by pg_start_backup() but is smoothed by default. -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
