Bug #102774 A scenario that result in memory leak
Submitted: 2 Mar 0:37 Modified: 6 Mar 7:13
Reporter: Haixing Weng (OCA) Email Updates:
Status: Verified Impact on me:
None 
Category:MySQL Server: DML Severity:S3 (Non-critical)
Version:5.7.31,8.0.22, 5.7.33 OS:Any
Assigned to: CPU Architecture:Any
Tags: memory leak;

[2 Mar 0:37] Haixing Weng
Description:
We usually gets memory overflow warning in our online system every several months.So we'd done some load testing in some scenario, and we found that even all tables of mysql are empty, the memory of mysql process will be growing at a slow rate (grow 25MB in 10 hours). 

How to repeat:
The cnf file had been attach below, use it to create a mysql process, and use sysbench to run a test loading oltp_read_only.lua.

1. create database sbtest;

2. prepare 6000 empty tables using sysbench

bin/sysbench --mysql-host=172.21.30.23 --mysql-port=61240 --mysql-user=hxdb --mysql-password=123456  --time=3600  --table_size=0 --report-interval=1 ./share/sysbench/oltp_read_only.lua --tables=6000 --table-size=0--threads=256 --mysql-ignore-errors=all --db-ps-mode=disable --luajit-cmd=off --thread-init-timeout=3600  prepare

3. run sysbench loading test

bin/sysbench --mysql-host=172.21.30.23 --mysql-port=61240 --mysql-user=hxdb --mysql-password=123456  --time=3600  --table_size=0 --report-interval=1 ./share/sysbench/oltp_read_only.lua --tables=6000 --table-size=0--threads=256 --mysql-ignore-errors=all --db-ps-mode=disable --luajit-cmd=off --thread-init-timeout=3600  run

4. using scripts or demo program to monitor $mysqld proc.RSS

5. we found that memory grows will nerver stop

6. I post our test result , with data & sampling graph
[2 Mar 0:39] Haixing Weng
memory sampling graph

Attachment: sampling.png (image/png, text), 36.09 KiB.

[2 Mar 0:39] Haixing Weng
memory sampling data

Attachment: 31818.pid.Rss (application/rss+xml, text), 532.00 KiB.

[2 Mar 11:33] Haixing Weng
Suggest to running loading test in a long time, by using --time=36000(10hours) or 360000(5days), We observed 200MB memory grows, running in serveral hours up to now, and it seems to nerver stop
[3 Mar 4:08] Haixing Weng
We still observe memory grows even we had started mysqld with jemalloc lib
[6 Mar 7:13] MySQL Verification Team
Hello Haixing Weng,

Thank you for the report and feedback.
Observed the issue with 5.7.33 build with provided configuration and sysbench load.

regards,
Umesh