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Commitf246ea3

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In caught-up logical walsender, sleep only in WalSndWaitForWal().
Before sleeping, WalSndWaitForWal() sends a keepalive if MyWalSnd->write< sentPtr. When the latest physical LSN yields no logical replicationmessages (a common case), that keepalive elicits a reply. Processingthe reply updates pg_stat_replication.replay_lsn. WalSndLoop() lacksthat; when WalSndLoop() slept, replay_lsn advancement could stall untilwal_receiver_status_interval elapsed. This sometimes stalledsrc/test/subscription/t/001_rep_changes.pl for up to 10s.Reviewed by Fujii Masao and Michael Paquier.Discussion:https://postgr.es/m/20200418070142.GA1075445@rfd.leadboat.com
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‎src/backend/replication/walsender.c

Lines changed: 11 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -1428,8 +1428,10 @@ WalSndWaitForWal(XLogRecPtr loc)
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/*
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* We only send regular messages to the client for full decoded
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* transactions, but a synchronous replication and walsender shutdown
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* possibly are waiting for a later location. So we send pings
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* containing the flush location every now and then.
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* possibly are waiting for a later location. So, before sleeping, we
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* send a ping containing the flush location. If the receiver is
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* otherwise idle, this keepalive will trigger a reply. Processing the
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* reply will update these MyWalSnd locations.
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*/
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if (MyWalSnd->flush<sentPtr&&
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MyWalSnd->write<sentPtr&&
@@ -2314,14 +2316,14 @@ WalSndLoop(WalSndSendDataCallback send_data)
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WalSndKeepaliveIfNecessary();
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/*
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* We don't block if not caught up, unless there is unsent data
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* pending in which case we'd better block until the socket is
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* write-ready. This test is only needed for the case where the
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* send_data callback handled a subset of the available data but then
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* pq_flush_if_writable flushed it all --- we should immediately try
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* to send more.
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* Block if we have unsent data. XXX For logical replication, let
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* WalSndWaitForWal() handle any other blocking; idle receivers need
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* its additional actions. For physical replication, also block if
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* caught up; its send_data does not block.
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*/
2324-
if ((WalSndCaughtUp&& !streamingDoneSending)||pq_is_send_pending())
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if ((WalSndCaughtUp&&send_data!=XLogSendLogical&&
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!streamingDoneSending)||
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pq_is_send_pending())
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{
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longsleeptime;
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intwakeEvents;

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