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Remember asking for feedback during walsender shutdown.

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Since 5a991ef8 we're explicitly asking for feedback from the receiving
side when shutting down walsender, if there's not yet replicated
data.

Unfortunately we didn't remember (i.e. set waiting_for_ping_response to
true) having asked for feedback, leading to scenarios in which replies
were requested at a high frequency.

I can't reproduce this problem on my laptop, I think that's because the
problem requires a significant TCP window to manifest due to the
!pq_is_send_pending() condition. But since this clearly is a bug, let's
fix it.  There's quite possibly more wrong than just this though.

While fiddling with WalSndDone(), I rewrote a hard to understand comment
about looking at the flush vs. the write position.

Reported-By: Nick Cleaton, Magnus Hagander
Author: Nick Cleaton
Discussion: CAFgz3kus=rC_avEgBV=+hRK5HYJ8vXskJRh8yEAbahJGTzF2VQ@mail.gmail.com
    CABUevExsjROqDcD0A2rnJ6HK6FuKGyewJr3PL12pw85BHFGS2Q@mail.gmail.com
Backpatch: 9.4, were 5a991ef8 introduced the use of feedback messages
    during shutdown.
This commit is contained in:
Andres Freund 2016-04-28 22:09:48 -07:00
parent 94a16531b3
commit 2e1b4adf39
1 changed files with 8 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
src/backend/replication/walsender.c
View File

@ -2486,13 +2486,14 @@ WalSndDone(WalSndSendDataCallback send_data)
send_data();
/*
* Check a write location to see whether all the WAL have successfully
* been replicated if this walsender is connecting to a standby such as
* pg_receivexlog which always returns an invalid flush location.
* Otherwise, check a flush location.
* To figure out whether all WAL has successfully been replicated, check
* flush location if valid, write otherwise. Tools like pg_receivexlog
* will usually (unless in synchronous mode) return an invalid flush
* location.
*/
replicatedPtr = XLogRecPtrIsInvalid(MyWalSnd->flush) ?
MyWalSnd->write : MyWalSnd->flush;
if (WalSndCaughtUp && sentPtr == replicatedPtr &&
!pq_is_send_pending())
{
@ -2503,7 +2504,10 @@ WalSndDone(WalSndSendDataCallback send_data)
proc_exit(0);
}
if (!waiting_for_ping_response)
{
WalSndKeepalive(true);
waiting_for_ping_response = true;
}
}
/*