Revert "When WalSndCaughtUp, sleep only in WalSndWaitForWal()."

This reverts commit 421685812290406daea58b78dfab0346eb683bbb.  It caused
idle physical walsenders to busy-wait, as reported by Fujii Masao.

Discussion: https://postgr.es/m/20200417054146[email protected]

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 0e933228fc9e59ed8cb2ff444f908c42d945eddc..0813c830269488034eca5a714210c4ecd14860f8 100644 (file)
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1428,10 +1428,8 @@ 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, 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.
+        * possibly are waiting for a later location. So we send pings
+        * containing the flush location every now and then.
         */
        if (MyWalSnd->flush < sentPtr &&
            MyWalSnd->write < sentPtr &&
@@ -2316,16 +2314,20 @@ WalSndLoop(WalSndSendDataCallback send_data)
        WalSndKeepaliveIfNecessary();
 
        /*
-        * Block if we have unsent data.  Let WalSndWaitForWal() handle any
-        * other blocking; idle receivers need its additional actions.
+        * 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.
         */
-       if (pq_is_send_pending())
+       if ((WalSndCaughtUp && !streamingDoneSending) || pq_is_send_pending())
        {
            long        sleeptime;
            int         wakeEvents;
 
            wakeEvents = WL_LATCH_SET | WL_EXIT_ON_PM_DEATH | WL_TIMEOUT |
-               WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE;
+               WL_SOCKET_READABLE;
 
            /*
             * Use fresh timestamp, not last_processing, to reduce the chance
@@ -2333,6 +2335,9 @@ 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,