On Tue, Aug 04, 2015 at 02:21:16PM +0900, Michael Paquier wrote:
> >> On Tue, Jul 28, 2015 at 5:57 PM, Christoph Berg <[email protected]> wrote:
> >> > for something between 10% and 20% of the devel builds for
> >> > apt.postgresql.org
> >> > (which happen every 6h if there's a git change, so it happens every few
> >> > days),
> >> > I'm seeing this:
> In test case 2, the failure happens to be that the standby did not
> have the time to replicate the database beforepromotion that has been
> created on the master. One possible explanation for this failure is
> that the standby has been promoted before all the WAL needed for the
> tests has been replayed, hence we had better be sure that the
> replay_location of the standby matches pg_current_xlog_location()
> before promotion.
> Perhaps the attached patch helps?
Thanks. In light of your diagnosis, I can reliably reproduce the failure by
injecting a sleep into XLogSendPhysical(). Your patch fixes the problem, but
it adds wal_receiver_status_interval (= 10s) stalls, doubling
src/bin/pg_rewind/t/001_basic.pl runtime on a fast system. (The standby
applies the final WAL quickly, then sleeps for wal_receiver_status_interval
before notifying the master.) The standby will apply any written, unapplied
WAL during promotion. Therefore, I plan to commit the attached
performance-neutral variant of your patch.
diff --git a/src/bin/pg_rewind/RewindTest.pm b/src/bin/pg_rewind/RewindTest.pm
index 22e5cae..a4c1737 100644
--- a/src/bin/pg_rewind/RewindTest.pm
+++ b/src/bin/pg_rewind/RewindTest.pm
@@ -222,12 +222,8 @@ recovery_target_timeline='latest'
'-l', "$log_path/standby.log",
'-o', "-p $port_standby", 'start');
- # Wait until the standby has caught up with the primary, by polling
- # pg_stat_replication.
- my $caughtup_query =
-"SELECT pg_current_xlog_location() = replay_location FROM pg_stat_replication
WHERE application_name = 'rewind_standby';";
- poll_query_until($caughtup_query, $connstr_master)
- or die "Timed out while waiting for standby to catch up";
+ # The standby may have WAL to apply before it matches the primary. That
+ # is fine, because no test examines the standby before promotion.
}
sub promote_standby
@@ -235,6 +231,12 @@ sub promote_standby
#### Now run the test-specific parts to run after standby has been
started
# up standby
+ # Wait for the standby to receive and write all WAL.
+ my $wal_received_query =
+"SELECT pg_current_xlog_location() = write_location FROM pg_stat_replication
WHERE application_name = 'rewind_standby';";
+ poll_query_until($wal_received_query, $connstr_master)
+ or die "Timed out while waiting for standby to receive and write WAL";
+
# Now promote slave and insert some new data on master, this will put
# the master out-of-sync with the standby. Wait until the standby is
# out of recovery mode, and is ready to accept read-write connections.
--
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