On Sun, Jun 10, 2012 at 10:34 PM, Fujii Masao <masao.fujii@xxxxxxxxx> wrote: > 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. We should not do this because Magnus is proposing the patch (http://archives.postgresql.org/pgsql-hackers/2012-06/msg00348.php) which breaks the above assumption at all. So we should introduce something like NOSYNC option. 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
