Re: Synchronous replication patch v2

On Sat, Nov 15, 2008 at 2:00 AM, Heikki Linnakangas
<heikki.linnakangas@enterprisedb.com> wrote:
> Fujii Masao wrote:
>>
>> Attached is the latest version of Synch Rep patch.
>
> Why do we need a separate XLogsndRqst variable in shared memory? Don't we
> always want to send the WAL up to the same point as we flush it?

It's because the backends flush and send the WAL concurrently. I mean that
the backend might request for the WAL to be sent up to the further point while
another backend is writing it. If that variable is not separated, the backend
cannot request until the former flushing finishes.

Regards,

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