On Mon, Dec 15, 2014 at 12:59 PM, Patrick Krecker <patr...@judicata.com> wrote:
> On Mon, Dec 15, 2014 at 9:12 AM, Joseph Kregloh <jkreg...@sproutloud.com> > wrote: > > Hello, > > > > I have a master multi slave streaming replication setup. One master and > two > > slaves. I need to do some maintenance on one of the slaves as one of the > > drives died however there is some other weird things going on in that > array > > that I would need to investigate. So I am expecting the machine to be > down > > at least two hours. > > > > I remember reading that if a master cannot connect to the slave it would > > hold the log file from shipping. Is there any other way to hold the file > > until the slave comes back online? Would it affect both slaves not > getting > > their files shipped over? > > > > The good thing is that the slave in question is not serving any > connections. > > > > From what I remember emptying out the archive_command would pause log > > shipping. Can the same be done by issuing a pg_stop_backup()? > > > > Thanks, > > -Joseph Kregloh > > I think you will need to change your archive_command so it saves the > WALs to a location reachable by both slaves and the master, and have > both slaves pull from the same location. I don't think > pg_stop_backup() is useful in this situation. > > Currently my archive_command is to a sh script which internally does an rsync. It actually rsyncs to both slaves and then a Barman location. If I fail the archive_command, then i'll have a problem because my primary slave serves read only queries, so it might start serving out stale data. What I was thinking is shipping the log files that would go to the second slave to another machine or location on the master. Then once I am done with the maintenance i'll move those files over to the incoming folder. That would give a hopefully contain all the WAL files for the slave to catch up. Any thoughts against this? > The master will hold the logs as long as archive_command fails [1]. To > the extent that archive_command involves connecting to the slave, then > yes, Postgres will hold the WAL archives while the slave is down. > There are (at least) two reasons that saving the archives to some > other location is useful: > > 1) You don't risk running out of disk on the master due to batched up > WALs if a slave goes down. > 2) The backup of logs can be used to aid in point-in-time recovery. > > [1] http://www.postgresql.org/docs/9.1/static/continuous-archiving.html >
