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MDEV-5533 - Backport Threadpool improvements from Percona Server


Hi Sergei,

Since MDEV-5533 is marked critical for 10.0.12 it is a good time to start
this discussion.

IIRC we agreed that our intention is to accept default value change for
thread_pool_max_threads into 10.0 and accept priority queue throttling
into 10.1.

So default value for thread_pool_max_threads has bumped in percona server
from 500 to 100 000. The reason is: deadlocks and uneven distribution of
worker threads between thread groups in case of stalled connections.

But the above is contradicting to suggestions in KB:
so ideally, there should be a single active thread for each CPU on the
If your application constantly pegs at 500 threads, it might be a
strong indicator for high contention in the application, and threadpool
does not help much.
One way to solve the problem would be to set thread_pool_max_threads to a
very high value, but this might be less than ideal, and negatively affect

Said the above, do you still think it is a good idea to raise default value
of thread_pool_max_threads? If so, what should KB article state wrt this