MySQL Bugs: #104523: Improve logging of GCS communication issues.

Bug #104523	Improve logging of GCS communication issues.
Submitted:	3 Aug 2021 14:44	Modified:	22 Nov 2021 16:14
Reporter:	Simon Mudd (OCA)	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Group Replication	Severity:	S4 (Feature request)
Version:	8.0.26	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	communication, group replication, improved logging

Description:
I had an issue with a gr member not being able to join the group.

The logging shows:
2021-07-22T11:26:33.913088Z 0 [ERROR] [MY-011735] [Repl] Plugin group_replication reported: '[GCS] Error connecting to the local group communication engine instance.'

This error is far from clear: it does not specify what the error is, and it does not specify what endpoint it was connecting to.

Improving the message would help.

I dived into the code and see one example of possible problems are TLS issues, in my case this was due to a firewall issue. In either case reporting the error in more detail would have helped diagnose and resolve the issue faster.

The same error message is also reported in 2 different places.

How to repeat:
start a gr member with connections blocked to the default port 33061.

Suggested fix:
Improve logging along the lines of:

2021-08-03T13:38:17.094549Z 0 [ERROR] [MY-011735] [Repl] Plugin group_replication reported: '[GCS] Error connecting to the local group communication engine instance at <hostname>:<port>.  Reason: xxxxx.

Where xxx should be the error number and text reported by the OS.

See: https://github.com/mysql/mysql-server/pull/354

Related:  bug#104526

Adjusted category and made a FR.

Hi Simon,

Thanks for the info, FR and PR. I believe the change is very sensible and that should be merged but let's see what GR team will say.

all best
Bogdan

Posted by developer:
 
Changelog entry added for MySQL 8.0.28:

Group Replication now logs operating system errors returned when there is a problem connecting to the local XCom instance, so it is easier to resolve issues such as a firewall blocking the connection.