LP #1693511: Percona Server 5.7 memory usage keeps growing with perf schema + thread pooling

**Reported in Launchpad by Kenn Takara last update 18-01-2018 08:11:53

Ran across this issue when running PMM with PXC 5.7 (reproed this with Percona Server 5.7.17 on Centos7 with THP disabled and with/without jemalloc)

The server has no activity except for PMM. The memory usage of the process grows until killed.

Repro case (does not require PMM):
(1) Start the server
(2) Run the following test script

#!/bin/bash

while true
do
mysql -Spath/to/socket.sock -uroot -e "SELECT EVENT_NAME FROM performance_schema.file_summary_by_event_name;" > /dev/null
done

What happens:
the memory usage keeps growing until the process or the script is killed

Expect:
The memory usage to stabilize at some point

=======================

This appears to be a combination of the performance schema and thread pooling. Here's the output from running top.

Output after starting the test script
performance_schema=ON
thread-handling=pool-of-threads

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2017-05-25-05:43:05 20260 kennt 20 0 4545832 393380 20408 S 0.0 10.2 0:02.07 mysqld
2017-05-25-05:43:08 20260 kennt 20 0 4545832 393380 20408 S 0.7 10.2 0:02.09 mysqld
>> started the test script
2017-05-25-05:43:11 20260 kennt 20 0 4562732 393908 20436 S 9.3 10.2 0:02.37 mysqld
2017-05-25-05:43:14 20260 kennt 20 0 4564292 434824 20436 S 43.3 11.2 0:03.67 mysqld
2017-05-25-05:43:17 20260 kennt 20 0 4564292 516656 20436 S 43.2 13.4 0:04.97 mysqld
2017-05-25-05:43:20 20260 kennt 20 0 4564292 557572 20436 S 42.7 14.4 0:06.25 mysqld
2017-05-25-05:43:23 20260 kennt 20 0 4564292 598488 20436 S 42.9 15.5 0:07.54 mysqld
2017-05-25-05:43:26 20260 kennt 20 0 4564292 639404 20436 S 42.9 16.5 0:08.83 mysqld
2017-05-25-05:43:29 20260 kennt 20 0 4564292 680320 20436 S 42.3 17.6 0:10.10 mysqld
(this will keep growing)
2017-05-25-05:44:05 20260 kennt 20 0 5023044 988.9m 20548 S 0.3 26.2 0:20.43 mysqld
2017-05-25-05:44:08 20260 kennt 20 0 5023044 991.2m 20728 S 0.3 26.3 0:20.44 mysqld

Output after starting the script with performance_schema=OFF
performance_schema=OFF
thread-handling=pool-of-threads

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2017-05-25-05:46:14 24348 kennt 20 0 4394072 260772 20308 S 0.3 6.7 0:01.87 mysqld
2017-05-25-05:46:20 24348 kennt 20 0 4394072 260772 20308 S 0.0 6.7 0:01.87 mysqld
>> started the test script
2017-05-25-05:46:20 24348 kennt 20 0 4412532 261300 20340 S 9.6 6.8 0:02.16 mysqld
2017-05-25-05:46:23 24348 kennt 20 0 4412532 261300 20340 S 11.0 6.8 0:02.49 mysqld
2017-05-25-05:46:26 24348 kennt 20 0 4412532 261300 20340 S 11.3 6.8 0:02.83 mysqld
2017-05-25-05:46:29 24348 kennt 20 0 4412532 261300 20340 S 11.3 6.8 0:03.17 mysqld
2017-05-25-05:46:32 24348 kennt 20 0 4412532 261300 20340 S 10.6 6.8 0:03.49 mysqld

Output after starting the script with thread-handling commented out
performance_schema=ON
#thread-handling=pool-of-threads

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2017-05-25-05:48:12 27277 kennt 20 0 4537668 393232 20424 S 0.3 10.2 0:02.00 mysqld
2017-05-25-05:48:15 27277 kennt 20 0 4537668 393232 20424 S 0.0 10.2 0:02.00 mysqld
>> started the test script
2017-05-25-05:48:18 27277 kennt 20 0 4537668 393480 20572 S 4.7 10.2 0:02.14 mysqld
2017-05-25-05:48:21 27277 kennt 20 0 4537668 393480 20572 S 43.0 10.2 0:03.43 mysqld
2017-05-25-05:48:24 27277 kennt 20 0 4537668 393480 20572 S 42.5 10.2 0:04.71 mysqld
2017-05-25-05:48:27 27277 kennt 20 0 4537668 393480 20572 S 42.5 10.2 0:05.99 mysqld
2017-05-25-05:48:30 27277 kennt 20 0 4537668 393480 20572 S 43.0 10.2 0:07.28 mysqld