The failing test case validates Seconds_Behind_Master for a delayed
slave, while STOP SLAVE is executed during a delay. The test fixes
initially added to the test (commit b04c857596) added a table lock
to ensure a transaction could not finish before validating the
Seconds_Behind_Master field after SLAVE START, but did not address a
possibility that the transaction could finish before running the
STOP SLAVE command, which invalidates the validations for the rest
of the test case. Specifically, this would result in 1) a timeout in
“Waiting for table metadata lock” on the replica, which expects the
transaction to retry after slave restart and hit a lock conflict on
the locked tables (added in b04c857596), and 2) that
Seconds_Behind_Master should have increased, but did not.
The failure can be reproduced by synchronizing the slave to the master
before the MDEV-32265 echo statement (i.e. before the SLAVE STOP).
This patch fixes the test by adding a mechanism to use DEBUG_SYNC to
synchronize a MASTER_DELAY, rather than continually increase the
duration of the delay each time the test fails on buildbot. This is
to ensure that on slow machines, a delay does not pass before the
test gets a chance to validate results. Additionally, it decreases
overall test time because the test can continue immediately after
validation, thereby bypassing the remainder of a full delay for each
transaction.
the test waits for the event to get stuck on MASTER_DELAY,
but on a slow/overloaded slave the event might pass MASTER_DELAY
before the test starts waiting.
Wait for the event to get stuck on the LOCK TABLES (after MASTER_DELAY),
the event cannot avoid that,
In an addition to test rpl.rpl_parallel_sbm added by MDEV-32265, the
test uses sleep statements alone to test Seconds_Behind_Master with
delayed replication. On slow running machines, the test can pass the
intended MASTER_DELAY duration and Seconds_Behind_Master can become
0, when the test expects the transaction to still be actively in a
delaying state.
This can be consistently reproduced by adding a sleep statement
before the call to
--let = query_get_value(SHOW SLAVE STATUS, Seconds_Behind_Master, 1)
to sleep past the delay end point.
This patch fixes this by locking the table which the delayed
transaction targets so Second_Behind_Master cannot be updated before
the test reads it for validation.
If a replica is actively delaying a transaction when restarted (STOP
SLAVE/START SLAVE), when the sql thread is back up,
Seconds_Behind_Master will present as 0 until the configured
MASTER_DELAY has passed. That is, before the restart,
last_master_timestamp is updated to the timestamp of the delayed
event. Then after the restart, the negation of sql_thread_caught_up
is skipped because the timestamp of the event has already been used
for the last_master_timestamp, and their update is grouped together
in the same conditional block.
This patch fixes this by separating the negation of
sql_thread_caught_up out of the timestamp-dependent block, so it is
called any time an idle parallel slave queues an event to a worker.
Note that sql_thread_caught_up is still left in the check for internal
events, as SBM should remain idle in such case to not "magically" begin
incrementing.
Reviewed By:
============
Andrei Elkin <andrei.elkin@mariadb.com>
MDEV-31749 sporadic assert in MDEV-30619 new test
If the workers of a parallel replica are busy (potentially with long
queues), but the SQL thread has no events left to distribute (so it
goes idle), then the next event that comes from the primary will
update mi->last_master_timestamp with its timestamp, even if the
workers have not yet finished.
This patch changes the parallel replica logic which updates
last_master_timestamp after idling from using solely sql_thread_caught_up
(added in MDEV-29639) to using the latter with rli queued/dequeued
event counters.
That is, if the queued count is equal to the dequeued count, it
means all events have been processed and the replica is considered
idle when the driver thread has also distributed all events.
Low level details of the commit include
- to make a more generalized test for Seconds_Behind_Master on
the parallel replica, rpl_delayed_parallel_slave_sbm.test
is renamed to rpl_parallel_sbm.test for this purpose.
- pause_sql_thread_on_next_event usage was removed
with the MDEV-30619 fixes. Rather than remove it, we adapt it
to the needs of this test case
- added test case to cover SBM spike of relay log read and LMT
update that was fixed by MDEV-29639
- rpl_seconds_behind_master_spike.test is made to use
the negate_clock_diff_with_master debug eval.
Reviewed By:
============
Andrei Elkin <andrei.elkin@mariadb.com>
