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
|
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
|
But the THREADS table only had:
MariaDB [test]> select name, thread_os_id from performance_schema.threads order by thread_os_id;
|
+-----------------------------------+--------------+
|
| name | thread_os_id |
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+-----------------------------------+--------------+
|
| thread/sql/main | 14728 |
|
| thread/mysys/statement_timer | 14729 |
|
| thread/aria/checkpoint_background | 14730 |
|
| thread/innodb/page_cleaner_thread | 14732 |
|
| thread/sql/manager | 14739 |
|
| thread/sql/binlog_background | 14740 |
|
| thread/sql/signal_handler | 14742 |
|
| thread/innodb/thread_pool_thread | 15299 |
|
| thread/sql/one_connection | 15383 |
|
+-----------------------------------+--------------+
|
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.
Bug
Major
