Re: Sync Rep: First Thoughts on Code

Hi,

On Thu, Dec 4, 2008 at 6:29 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> The only sensible settings are
> synchronous_commit = on, synchronous_replication = on
> synchronous_commit = on, synchronous_replication = off
> synchronous_commit = off, synchronous_replication = off
>
> This doesn't make any sense: (does it??)
> synchronous_commit = off, synchronous_replication = on

If the standby replies before writing the WAL, that strategy can improve
the performance with moderate reliability, and sounds sensible.
IIRC, MySQL Cluster might use that strategy.

> I was expecting you to have walreceiver and startup share an end of WAL
> address via shared memory, so that startup never tries to read past end.
> That way we would be able to begin reading a WAL file *before* it was
> filled. Waiting until a file fills means we still have to have
> archive_timeout set to ensure we switch regularly.

You mean that not pg_standby but startup process waits for the next
WAL available? If so, I agree with you in the future. That is, I just think
that this is next TODO because there are many problems which we
should resolve carefully to achieve it. But, if it's essential for 8.4, I will
tackle it. What is your opinion? I'd like to clear up the goal for 8.4.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center