- thread_pool_size command line option upper limit increased to 100 000
(same as for max_connections)
- thread_pool_size system variable upper limit is maximum of 128 or
the value given at command line
- thread groups are now allocated dynamically
Different limit for command line option and system variable was done to
avoid additional mutex for all_groups and threadpool_max_size.
To allow it, change minimum of thread_pool_stall_limit to be 10 milliseconds.
Also introduce a new parameter to oversubscribe a group . Number of threads running in parallel would be higher than it normally should, leading to thrashing, but it may improving preemptiveness, which is useful for the described corner case.
