On Wed, Jun 6, 2012 at 8:26 PM, Fujii Masao <masao.fu...@gmail.com> wrote: > On Tue, Jun 5, 2012 at 11:44 PM, Magnus Hagander <mag...@hagander.net> wrote: >> On Tue, Jun 5, 2012 at 4:42 PM, Fujii Masao <masao.fu...@gmail.com> wrote: >>> On Tue, Jun 5, 2012 at 9:53 PM, Magnus Hagander <mag...@hagander.net> wrote: >>>> Right now, pg_receivexlog sets: >>>> replymsg->write = InvalidXLogRecPtr; >>>> replymsg->flush = InvalidXLogRecPtr; >>>> replymsg->apply = InvalidXLogRecPtr; >>>> >>>> when it sends it's status updates. >>>> >>>> I'm thinking it sohuld set replymsg->write = blockpos instad. >>>> >>>> Why? That way you can see in pg_stat_replication what has actually >>>> been received by pg_receivexlog - not just what we last sent. This can >>>> be useful in combination with an archive_command that can block WAL >>>> recycling until it has been saved to the standby. And it would be >>>> useful as a general monitoring thing as well. >>>> >>>> I think the original reason was that it shouldn't interefer with >>>> synchronous replication - but it does take away a fairly useful >>>> usecase... >>> >>> I think that not only replaymsg->write but also ->flush should be set to >>> blockpos in pg_receivexlog. Which allows pg_receivexlog to behave >>> as synchronous standby, so we can write WAL to both local and remote >>> synchronously. I believe there are some use cases for synchronous >>> pg_receivexlog. >> >> pg_receivexlog doesn't currently fsync() after every write. It only >> fsync():s complete files. So we'd need to set ->flush only at the end >> of a segment, right? > > Yes. > > Currently the status update is sent for each status interval. In sync > replication, transaction has to wait for a while even after pg_receivexlog > has written or flushed the WAL data. > > So we should add new option which specifies whether pg_receivexlog > sends the status packet back as soon as it writes or flushes the WAL > data, like the walreceiver does?
That might be useful, but I think that's 9.3 material at this point. But I think we can get the "set the write location" in as a bugfix. -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
