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When WalSndCaughtUp, sleep only in WalSndWaitForWal(). 

Before sleeping, WalSndWaitForWal() sends a keepalive if MyWalSnd->write
< sentPtr.  That is important in logical replication.  When the latest
physical LSN yields no logical replication messages (a common case),
that keepalive elicits a reply, and processing the reply updates
pg_stat_replication.replay_lsn.  WalSndLoop() lacks that; when
WalSndLoop() slept, replay_lsn advancement could stall until
wal_receiver_status_interval elapsed.  This sometimes stalled
src/test/subscription/t/001_rep_changes.pl for up to 10s.

Discussion: https://postgr.es/m/20200406063649.GA3738151@rfd.leadboat.com
This commit is contained in:
Noah Misch 2020-04-11 10:30:00 -07:00
parent 969f9d0b4b
commit 4216858122
1 changed files with 8 additions and 13 deletions
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21
src/backend/replication/walsender.c
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@ -1428,8 +1428,10 @@ WalSndWaitForWal(XLogRecPtr loc)
/*
* We only send regular messages to the client for full decoded
* transactions, but a synchronous replication and walsender shutdown
* possibly are waiting for a later location. So we send pings
* containing the flush location every now and then.
* possibly are waiting for a later location. So, before sleeping, we
* send a ping containing the flush location. If the receiver is
* otherwise idle, this keepalive will trigger a reply. Processing the
* reply will update these MyWalSnd locations.
*/
if (MyWalSnd->flush < sentPtr &&
MyWalSnd->write < sentPtr &&
@ -2314,20 +2316,16 @@ WalSndLoop(WalSndSendDataCallback send_data)
WalSndKeepaliveIfNecessary();
/*
* We don't block if not caught up, unless there is unsent data
* pending in which case we'd better block until the socket is
* write-ready. This test is only needed for the case where the
* send_data callback handled a subset of the available data but then
* pq_flush_if_writable flushed it all --- we should immediately try
* to send more.
* Block if we have unsent data. Let WalSndWaitForWal() handle any
* other blocking; idle receivers need its additional actions.
*/
if ((WalSndCaughtUp && !streamingDoneSending) || pq_is_send_pending())
if (pq_is_send_pending())
{
long sleeptime;
int wakeEvents;
wakeEvents = WL_LATCH_SET | WL_EXIT_ON_PM_DEATH | WL_TIMEOUT |
WL_SOCKET_READABLE;
WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE;
/*
* Use fresh timestamp, not last_processing, to reduce the chance
@ -2335,9 +2333,6 @@ WalSndLoop(WalSndSendDataCallback send_data)
*/
sleeptime = WalSndComputeSleeptime(GetCurrentTimestamp());
if (pq_is_send_pending())
wakeEvents |= WL_SOCKET_WRITEABLE;
/* Sleep until something happens or we time out */
(void) WaitLatchOrSocket(MyLatch, wakeEvents,
MyProcPort->sock, sleeptime,