we have a customer that has observed problems related to the interaction of the thread pools in mariadb 5.5.30 and tokudb 7.1.0. the problem is that connections that stuck for 100's of seconds in the Killed state when a big tokudb transaction commit is in progress. the customer claims that this problem was resolved by turning the thread pool OFF. have there been any fixes to the thread pool implementation post the 5.5.30 release? here is some information that may be useful. the processlist showed 2838 client connections of which: 851 Killed 483 Sleep 1467 Connect 1 show processlist 1 processing a commit on a big delete from a tokudb table 35 blocked on a row lock held by the big delete the Killed connections look like: 84847752 sfi_mysql 10.0.0.60:1814 sfi Killed 93 NULL 0.000 with the connection address and time slightly different a gdb snapshot of the system at the time of the failure: 291 total threads 130 threads waiting on fil_aio_wait 52 threads waiting on tokudb's work_on_kibbutz 16 thread tokudb deserialization thread waiting 36 mysql update thread blocked on the tokudb lock tree 1thread executing a big tokudb delete transaction 40 threads in the thread pool get_event function 1 tokudb checkpoint thread blocked waiting for the LP MO lock, which is held by the big txn commit thread that leaves 15 misc worker threads that are not doing anything interesting the gdb stacks for the thread pool threads are: Thread 78 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 71 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 70 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 69 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 68 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 62 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 57 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 52 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 51 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 49 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 45 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 44 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 43 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 42 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 41 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 39 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 37 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 36 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 35 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 33 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 32 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 31 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 26 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 24 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 22 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 21 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 20 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 19 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 18 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 17 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 16 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 13 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 12 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 11 : epoll_wait , io_poll_wait , listener , get_event , worker_main , start_thread , clone Thread 8 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 7 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 5 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 4 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 3 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone Thread 2 : pthread_cond_timedwait@@GLIBC_2.3.2 , inline_mysql_cond_timedwait , get_event , worker_main , start_thread , clone thanks rich prohaska