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MDEV-36840 Seconds_Behind_Master Spike at Log Rotation on Parallel Replica

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`Seconds_Behind_Master` unsets from 0 when a
parallel replica processes an internal event.

Est. 8dad51481b of MDEV-10653, the idle status of the worker
threads directly checks the emptiness of the workers’ queue.
The problem is that the queue could be entirely
internal events that don’t record replicated content.

In contrast, the (main) SQL thread (in both serial and parallel
replicas) uses a state boolean `sql_thread_caught_up` that is
not unset if the event is internal. Therefore, this patch adds
a workers’ equivalent, `worker_threads_caught_up`, that
matches the behaviour of that for the (main) SQL thread.

Reviewed-by: Brandon Nesterenko <brandon.nesterenko@mariadb.com>
Acked-by: Kristian Nielsen <knielsen@knielsen-hq.org>
This commit is contained in:
ParadoxV5
2025-07-07 13:01:24 -06:00
parent 8a45128106
commit f7ba16980d
4 changed files with 61 additions and 27 deletions
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20
sql/rpl_parallel.cc
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@@ -3069,13 +3069,21 @@ rpl_parallel::stop_during_until()
}
bool
rpl_parallel::workers_idle(Relay_log_info *rli)
bool Relay_log_info::are_sql_threads_caught_up()
{
mysql_mutex_assert_owner(&rli->data_lock);
return !rli->last_inuse_relaylog ||
rli->last_inuse_relaylog->queued_count ==
rli->last_inuse_relaylog->dequeued_count;
mysql_mutex_assert_owner(&data_lock);
if (!sql_thread_caught_up)
return false;
/*
The SQL thread sets @ref worker_threads_caught_up to `false` but not `true`.
Therefore, this place needs to check if it can now be `true`.
*/
if (!worker_threads_caught_up && ( // No need to re-check if already `true`.
!last_inuse_relaylog || // `nullptr` case
last_inuse_relaylog->queued_count == last_inuse_relaylog->dequeued_count
))
worker_threads_caught_up= true; // Refresh
return worker_threads_caught_up;
}