On Sun, Jun 10, 2012 at 9:25 PM, Fujii Masao <masao.fujii@xxxxxxxxx> wrote: > On Sun, Jun 10, 2012 at 7:43 PM, Magnus Hagander <magnus@xxxxxxxxxxxx> wrote: >> On Sat, Jun 9, 2012 at 2:51 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: >>> Fujii Masao <masao.fujii@xxxxxxxxx> writes: >>>> This seems a bug. I think we should prevent pg_basebackup from >>>> becoming synchronous standby. Thought? >>> >>> Absolutely. If we have replication clients that are not actually >>> capable of being standbys, there *must* be a way for the master >>> to know that. >> >> I thought we fixed this already by sending InvalidXlogRecPtr as flush >> location? And that this only applied in 9.2? >> >> Are you saying we picked pg_basebackup *in backup mode* (not log >> streaming) as synchronous standby? > > Yes. > >> If so then yes, that is >> *definitely* a bug that should be fixed. We should never select a >> connection that's not even streaming log as standby! > > Agreed. Attached patch prevents pg_basebackup from becoming sync > standby. Also this patch fixes another problem: currently only walsender > which reaches STREAMING state can become sync walsender. OTOH, > sync walsender thinks that walsender with higher priority will be sync one > whether its state is STREAMING, and switches to potential sync walsender. > So when the standby with higher priority connects to the master, we > might have no sync standby until it reaches the STREAMING state. > To fix this problem, the patch switches walsender's state from sync to > potential *after* walsender with higher priority has reached the > STREAMING state. > > We also should not select (1) background stream process forked from > pg_basebackup and (2) pg_receivexlog as sync standby because they > don't send back replication progress. To address this, I'm thinking to > introduce new option "NOSYNC" in "START_REPLICATION" command > as follows, and to change (1) and (2) so that they specify NOSYNC. > > START_REPLICATION XXX/XXX [NOSYNC] > > If the standby specifies NOSYNC option, it's never assigned as sync > standby even if its name is in synchronous_standby_names. Thought? The standby which always sends InvalidXLogRecPtr back should not become sync one. So instead of NOSYNC option, by checking whether InvalidXLogRecPtr is sent, we can avoid problematic sync standby. Regards, -- Fujii Masao -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
