MIN_TIMER_WAIT field is inconsistent for wait/synch/cond/rocksdb/cond_stop about mysql-5.6

[hermanlee]

Comment by maykov
Monday Jul 20, 2015 at 23:52 GMT

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Example of the failure:
===========
$mysqltest.sh --perfschema perfschema.aggregate --repeat=5
.....
CURRENT_TEST: perfschema.aggregate
--- /data/users/maykov/mysql/5.6/mysql-test/suite/perfschema/r/aggregate.result 2015-07-20 22:21:42.424748049 +0300
+++ /data/users/maykov/mysql/5.6/_build-5.6-Debug-PerfSchema/mysql-test/var/log/aggregate.reject 2015-07-21 02:30:39.323111516 +0300
@@ -86,6 +86,7 @@
HAVING (e.MAX_TIMER_WAIT < MAX(i.MAX_TIMER_WAIT))
OR @dump_all;
EVENT_NAME MAX_TIMER_WAIT MAX(i.MAX_TIMER_WAIT)
+wait/synch/cond/rocksdb/cond_stop 0 1001177278010
"Verifying waits aggregate consistency (thread)"
SELECT EVENT_NAME, e.SUM_TIMER_WAIT, SUM(t.SUM_TIMER_WAIT)
FROM performance_schema.events_waits_summary_global_by_event_name AS e

mysqltest: Result content mismatch

Some observations: innodb doesn't use conditions to stop background threads it is running. Instead, it is running threads like this while (srv_shutdown_state == SRV_SHUTDOWN_NONE) {do stuff}. This is not ideal for us for two reasons:

1. It might break on some machine architecture (which we might never run on anyway)
2. Rocksdb plugin waits for the condition or a timeout. So, the wait doesn't consume CPU and stops right away upon server shutdown.
   At this point, moving to innodb way would simplify things but will be a regression.

I think, this bug is not specific to MyRocks but probably somewhere in the server. We do not do anything special with conditions and aggregation counters. I'm going to stop exposing PFS about conditions which will fix this test.

[hermanlee]

Comment by yoshinorim
Tuesday Jul 21, 2015 at 15:52 GMT

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WebScaleSQL disables performance schema by default, so I think it's fine to ignore for the time being.

[hermanlee]

Comment by jtolmer
Tuesday Jul 21, 2015 at 16:28 GMT

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WebScaleSQL and FB-MySQL both intentionally test with PerfSchema enabled in order to make sure that we're not building up a lot of debt of broken functionality.

[hermanlee]

Comment by spetrunia
Tuesday Jul 21, 2015 at 20:07 GMT

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AFAIK, the values are in picoseconds. They are not in CPU ticks, because one can use different timers for measurements (see setup_timers )

[gunnarku]

Obsolete.