On Thu, Mar 25, 2010 at 11:37 AM, Peter Geoghegan
<peter.geoghegan86 at gmail.com> wrote:
> I am aware that it's possible to specify whether or not
> synchronous_commit is used on a transaction by transaction basis, but
> it isn't apparent how I can do this with the Qt database driver that I
> use, that wraps libpq. I'm using implicit transactions by calling
> pl/pgSQL functions on the slaves (every modifying operation is a
> function call). Perhaps that should be the next thing I investigate if
> turning synchronous_commit off server wide in postgresql.conf on
> slaves turns out to be a bad idea.
>

Can you run arbitrary queries via your Qt wrapper?  If so, then run a
"SET SESSION" disable of the synchronous commit, not per-transaction.
Then you get the benefit of it for that whole session without having
to enable it globally.

I'm not sure the effect it would have on the replica to enable it
globally -- ie, if the master is notified that a sync event was
committed, but it infact gets "undone" on crash, will it replay?  I
wouldn't count on it without thorough code review and testing.