On Wed, Feb 23, 2011 at 11:49 AM, Greg Smith <g...@2ndquadrant.com> wrote: > Robert Haas wrote: >>> >>> 2. Synchronous replication. Splitting up this patch has allowed some > On top of 4 listed reviewers I know Dan Farina is poking at the last update, > so we may see one more larger report on top of what's already shown up. And > Jaime keeps kicking the tires too. What Simon was hoping is that a week of > others looking at this would produce enough feedback that it might be > possible to sweep the remaining issues up soon after he's back. It looks to > me like that's about when everything else that's still open will probably > settle too.
Besides some of the fixable issues, I am going to have to echo Robert's sentiments about a few kinks that go beyond mechanism in the syncrep patch: in particular, it will *almost* solve the use case I was hoping to solve: a way to cleanly perform planned switchovers between machines with minimal downtime and no lost data. But there are a couple of holes I have thought of so far: 1. The 2-safe methodology supported is not really compatible with performing planned-HA-switchover of a cluster with its own syncrep guarantees on top of that. For example: Server A syncreps to Server B Now I want to provision server A-prime, which will eventually take the place of A. Server A syncreps to Server B Server A syncreps to Server A-prime Right now, as it stands, the syncrep patch will be happy as soon as the data has been fsynced to either B or A-prime; I don't think we can guarantee at any point that A-prime can become the leader, and feed B. 2. The unprivileged user can disable syncrep, in any situation. This flexibility is *great*, but you don't really want people to do it when one is performing the switchover. Rather, in a magical world we'd hope that disabling syncrep would just result in not having to synchronously commit to B (but, in this case, still synchronously commit to A-prime) In other words, to my mind, you can use syncrep as-is to provide 2-safe durability xor a scheduled switchover: as soon as someone wants both, I think they'll have some trouble. I do want both, though. -- fdr -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
