On Sat, Jan 22, 2011 at 8:31 AM, Simon Riggs <si...@2ndquadrant.com> wrote: > On Fri, 2011-01-21 at 13:32 -0500, Robert Haas wrote: > >> One idea might be to wait both before and after commit. If >> allow_standalone_primary is off, and a commit is attempted, we check >> whether there's a slave connected, and if not, wait for one to >> connect. Then, we write and sync the commit WAL record. Next, we >> wait for the WAL to be ack'd. Of course, the standby might disappear >> between the first check and the second, but it would greatly reduce >> the possibility of the master being ahead of the standby after a >> crash, which might be useful for some people. > > I like this idea. > > I think it would be too invasive to make a check before we insert each > WAL record, as Aidan suggests. Even if we did that, you aren't protected > when a standby goes down because you'll still have written half a > transaction and still be waiting. > > So I propose that > > if (!allow_standalone_primary) > ConfirmSyncRepAvailable(); > > before PreCommit_Notify(). That puts transaction into a wait state that > lasts until a sync rep standby is available. Note that it is before the > actual commit, so if we decide we need to we can cancel those > transactions and have them properly abort. > > I won't add that code yet, in case better ideas emerge. > > There is no support for preventing connections at startup, so I will > remove that completely, now.
Time's running short - do you have an updated patch? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
