MySQL Bugs: #86863: thread pool spams error log on connection failure.

Bug #86863	thread pool spams error log on connection failure.
Submitted:	29 Jun 2017 6:31	Modified:	12 Jan 2018 19:29
Reporter:	Shane Bester (Platinum Quality Contributor)	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Errors	Severity:	S3 (Non-critical)
Version:	5.6.36, 5.7.18	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	regression, thread pool

Description:
When invalid user/host tries to connect to mysql with thread pool plugin, we get too much spam in the logs.

With thread pool:
-----------------
[Warning] Hostname 'i7' does not resolve to '192.168.1.107'.
[Note] Hostname 'i7' has the following IP addresses:
[Note]  - 127.0.0.1
[ERROR] Failed to prepare connection
[Warning] Failed to create thd and authenticate connection
[Warning] Failed to process connection event
[ERROR] Failed to prepare connection
[Warning] Failed to create thd and authenticate connection
[Warning] Failed to process connection event
[Note] Access denied for user 'root'@'localhost' (using password: YES)
[ERROR] Failed to prepare connection
[Warning] Failed to create thd and authenticate connection
[Warning] Failed to process connection event

Without thread pool:
-------------------
[Warning] Hostname 'i7' does not resolve to '192.168.1.107'.
[Note] Hostname 'i7' has the following IP addresses:
[Note]  - 127.0.0.1
[Note] Access denied for user 'root'@'localhost' (using password: YES)

How to repeat:
here was my test:

E:\mysql-5.7.17-winx64\bin>mysql -uroot -h192.168.1.107
ERROR 1130 (HY000): Host '192.168.1.107' is not allowed to connect to this MySQL server

E:\mysql-5.7.17-winx64\bin>mysql -uroot -h192.168.1.107
ERROR 1130 (HY000): Host '192.168.1.107' is not allowed to connect to this MySQL server

E:\mysql-5.7.17-winx64\bin>mysql -uroot -p12345
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)

Suggested fix:
lowering log_warnings is not an option because logging misses vital info then.
please reduce the thread pool's output to at most one informative line per event.

The issue also occurs in MySQL 5.6.37.

Is there any workaround apart from disabling log_warnings variable?

One workaround is to disable the thread pool plugin..

Posted by developer:
 
Fixed in 5.5.60, 5.6.40, 5.7.22, 8.0.5, 9.0.0.

The thread pool plugin logged too much information for failed connections.

Now https://bugs.mysql.com/bug.php?id=90618 has been filed on 5.7.22