Details
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Bug
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Status: Closed (View Workflow)
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Major
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Resolution: Fixed
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10.6.17, 11.4.1
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None
Description
While actually trying to analyze something else I found that PERFORMANCE_SCHEMA.THREADS does not list all server threads.
In my case I was originally looking for InnoDB background encryption threads, of which I had four configured, but found that there were actually five threads missing.
ps showed:
$ pgrep -w mariadbd | xargs ps -Lo pid,lwp,cmd
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PID LWP CMD
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14728 14728 /usr/sbin/mariadbd
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14728 14729 /usr/sbin/mariadbd
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14728 14730 /usr/sbin/mariadbd
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14728 14731 /usr/sbin/mariadbd
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14728 14732 /usr/sbin/mariadbd
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14728 14735 /usr/sbin/mariadbd
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14728 14736 /usr/sbin/mariadbd
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14728 14737 /usr/sbin/mariadbd
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14728 14738 /usr/sbin/mariadbd
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14728 14739 /usr/sbin/mariadbd
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14728 14740 /usr/sbin/mariadbd
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14728 14742 /usr/sbin/mariadbd
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14728 15299 /usr/sbin/mariadbd
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14728 15383 /usr/sbin/mariadbd
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But the THREADS table only had:
MariaDB [test]> select name, thread_os_id from performance_schema.threads order by thread_os_id;
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+-----------------------------------+--------------+
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| name | thread_os_id |
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+-----------------------------------+--------------+
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| thread/sql/main | 14728 |
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| thread/mysys/statement_timer | 14729 |
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| thread/aria/checkpoint_background | 14730 |
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| thread/innodb/page_cleaner_thread | 14732 |
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| thread/sql/manager | 14739 |
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| thread/sql/binlog_background | 14740 |
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| thread/sql/signal_handler | 14742 |
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| thread/innodb/thread_pool_thread | 15299 |
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| thread/sql/one_connection | 15383 |
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+-----------------------------------+--------------+
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So LWP ides 14731 and 14835-14738 were missing. The later four are the background encryption threads, and 14731 was running this according to gdb:
Thread 4 (Thread 0x7fa945118700 (LWP 14731)):
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#0 syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
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#1 0x000055faa5f1213d in my_getevents (min_nr=1, nr=256, ev=0x7fa945115d60, ctx=<optimized out>) at ./tpool/aio_linux.cc:105
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#2 tpool::aio_linux::getevent_thread_routine (aio=0x55faa8c4e650) at ./tpool/aio_linux.cc:105
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#3 0x00007fa96107bdf4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
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#4 0x00007fa961195609 in start_thread (arg=<optimized out>) at pthread_create.c:477
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#5 0x00007fa960d81353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
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Not sure whether it is only these threads that do not show, or whether there are also other candidates that were just not running in this setup to begin with.
Attachments
Issue Links
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Activity
tpool::aio_linux::getevent_thread_routine is actually using wlad’s thread pool, yet it does not appear in performance_schema. Once that has been sorted out, it should be rather straightforward to make the encryption threads (actually flag-pages-dirty threads) use the thread pool.
a2f510fccff23e5011486c240587b8f1a98ecacc makes the aio completion thread to appear as "innodb background thread" in PS
The rest is now Innodb's
I added thread/innodb/page_encrypt_thread for fil_crypt_thread. Everything else seemed to be covered already; only thread/innodb/thread_pool_thread was apparently missing some cases. These labels but not the thread counts are being checked in the test perfschema.threads_innodb.
because encryption threads are created using std::thread which completely bypasses perfschema.
should be converted to use the thread pool, I presume