> > Hello everyone, > > Two questions, grateful for any feedback anyone can share. They relate to > switchover between master and hot-standby. > > > 1. What exactly is the behaviour of the master/primary during shutdown > when it has a hot standby? > > https://wiki.postgresql.org/wiki/Hot_Standby > http://www.postgresql.org/docs/current/static/hot-standby.html > > If I shut down the master, then afterwards when it is finished, I shut > down the standby, will they contain identical logical databases & WAL > records, e.g. assuming possible network failure? > > i.e. > - Is the primary shutdown delayed until it has received notice from the > standby that all WAL has been received? ( my guess is: no) > - Is the primary shutdown delayed until it has received notice from the > standby that all WAL has been applied? ( my guess is: no) > - Can the primary generate any new WAL (e.g. checkpoint) or logical data > changes during the shutdown process that might not be sent to the standby? > (my guess is: no) > > For example, > https://vibhorkumar.wordpress.com/2014/06/30/switchoverswitchback-in-postgresql-9-3/ > "With this patch, the walsender process tries to send all outstanding WAL > records to the standby in replication when the user shuts down the > master." > "tries"? > > That page also makes it seem like you have to manually check the WAL > status. (section 2) > Is there any way to make the primary's completion of shutdown > automatically synchronous with completion of WAL on standby(s)? What you used for you repltación? aplication u other. > > 2. Let's assume for the moment I have some crazy reason to prefer to avoid > rsync where possible, such as its historical weird behaviour on HFS+ > filesystems or its present unreliable heuristic for syncing hard-links or > its default behaviour of not using checksums. Can a controlled switchover > (not failover) be built on wal_keep_segments alone? > > wal_keep_segments could be set to a fairly high number, maybe 10000 > (160GB) to allow standby catchup even after a day. Let's assume here than > 99% of maintenance takes less than an hour, and that we're keeping rsync > as a fallback for the worst case. > > e.g. here's the whole switchover process... > > shutdown A (Master) > shutdown B (Standby) > (A and B should be identical in terms of WAL and logical data at this > point). > swap M/S configurations around > start B (Master) > > do some work on A for an hour > finish work on A > > start A (Standby) > A catches up with B from wal_keep_segments. > > > shutdown B (Master) > shutdown A (Standby) > (A and B should be identical in terms of WAL and logical data at this > point). > swap M/S configurations around > start A (Master) > start B (Standby) > Remeber init the slave igual firt moment. > Graeme Bell > > > > > -- > Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-admin--- > This message was processed by Kaspersky Mail Gateway 5.6.28/RELEASE > running at host imx2.etecsa.cu > Visit our web-site: <http://www.kaspersky.com>, <http://www.viruslist.com> > Saludos, Gilberto Castillo La Habana, Cuba
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