On Thu, Mar 17, 2022 at 7:14 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Thu, Mar 17, 2022 at 12:27 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > On Wed, Mar 16, 2022 at 7:38 PM Masahiko Sawada <sawada.m...@gmail.com> > > wrote: > > > > > > After more thought, can we check only wal_sender_timeout without > > > skip-count? That is, in WalSndUpdateProgress(), if we have received > > > any reply from the subscriber in last (wal_sender_timeout / 2), we > > > don't need to do anything in terms of keep-alive. If not, we do > > > ProcessRepliesIfAny() (and probably WalSndCheckTimeOut()?) then > > > WalSndKeepalivesIfNecessary(). That way, we can send keep-alive > > > messages every (wal_sender_timeout / 2). And since we don't call them > > > for every change, we would not need to worry about the overhead much. > > > > > > > But won't that lead to a call to GetCurrentTimestamp() for each change > > we skip? IIUC from previous replies that lead to a slight slowdown in > > previous tests of Wang-San. > > > If the above is true then I think we can use a lower skip_count say 10 > along with a timeout mechanism to send keepalive message. This will > help us to alleviate the overhead Wang-San has shown.
Using both sounds reasonable to me. I'd like to see how much the overhead is alleviated by using skip_count 10 (or 100). > BTW, I think there could be one other advantage of using > ProcessRepliesIfAny() (as you are suggesting) is that it can help to > release sync waiters if there are any. I feel that would be the case > for the skip_empty_transactions patch [1] which uses > WalSndUpdateProgress to send keepalive messages after skipping empty > transactions. +1 Regards, [1] https://www.postgresql.org/message-id/OS3PR01MB6275DFFDAC7A59FA148931529E209%40OS3PR01MB6275.jpnprd01.prod.outlook.com -- Masahiko Sawada EDB: https://www.enterprisedb.com/
