Hi, On Fri, Sep 25, 2009 at 7:10 PM, Heikki Linnakangas <heikki.linnakan...@enterprisedb.com> wrote: > Fujii Masao wrote: >> On Thu, Sep 24, 2009 at 7:57 PM, Heikki Linnakangas >> <heikki.linnakan...@enterprisedb.com> wrote: >>>>> - I know I said we should have just asynchronous replication at first, >>>>> but looking ahead, how would you do synchronous? >>>> As the previous patch did, I'm going to make walsender read the latest >>>> XLOG from wal_buffers, introduce the signaling between a backend >>>> and walsender, and keep a backend waiting until the specified XLOG >>>> has been written or fsynced in the standby. >>> Ok. I don't think walsender needs to access wal_buffers even then, >>> though. Once the backend has written the WAL, walsender can well read it >>> from disk (it will surely be in OS cache still). >> >> I think that walsender should not delay sending the XLOG until it has >> been written by the backend, for performance improvement. Otherwise, >> XLOG write and send are performed in serial, which would increase a >> response time. Should those be performed in parallel? > > Well, sure, performance is good, but let's keep it simple for now. The > write() to disk should normally be absorbed by the OS cache and return > quickly, so it's not a big delay.
Umm... a backend at least should tell walsender the location which it has written the XLOG before issuing fsync. In the current XLogWrite(), XLogCtl->LogwrtResult.Write is updated after fsync has been performed. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
