Re: Configuring synchronous replication

Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> On Fri, 2010-09-17 at 21:20 +0900, Fujii Masao wrote:
>> What synchronization level does each combination of sync_replication
>> and sync_replication_service lead to?
>
> There are only 4 possible outcomes. There is no combination, so we don't
> need a table like that above.
>
> The "service" specifies the highest request type available from that
> specific standby. If someone requests a higher service than is currently
> offered by this standby, they will either
> a) get that service from another standby that does offer that level
> b) automatically downgrade the sync rep mode to the highest available.

I like the a) part, I can't say the same about the b) part. There's no
reason to accept to COMMIT a transaction when the requested durability
is known not to have been reached, unless the user said so.

> For example, if you request recv but there is only one standby and it
> only offers async, then you get downgraded to async.

If so you choose, but with a net slowdown as you're now reaching the
timeout for each transaction, with what I have in mind, and I don't see
how you can avoid that. Even if you setup the replication from the
master, you still can mess it up the same way, right?

Regards,
--
dim