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. 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] - https://www.postgresql.org/message-id/CAFPTHDYvRSyT5ppYSPsH4Ozs0_W62-nffu0%3DmY1%2BsVipF%3DUN-g%40mail.gmail.com -- With Regards, Amit Kapila.
