MySQL Bugs: #101114: MySQL group replication not set read

Bug #101114	MySQL group replication not set read_only before it joins the GR cluster
Submitted:	10 Oct 2020 6:46	Modified:	14 Nov 2020 16:46
Reporter:	Wei Zhao (OCA)	Email Updates:
Status:	No Feedback	Impact on me:	None
Category:	MySQL Server: Group Replication	Severity:	S2 (Serious)
Version:	8.0.18	OS:	Any
Assigned to:	MySQL Verification Team	CPU Architecture:	Any

Description:
MGR has a bug that can cause data divergence, this is how to reproduce it:

0. setup an MGR cluster, whose primary node is M
1. kill M's mysqld process so that M drops out of the MGR cluster.
2. M's mysqld process is restarted by its mysqld_safe parent process automatically
3. Rejoin M to the MGR cluster by connecting to it and issue 'start group_replication' stmt.

there is a short window between step #2 and step #3 where M is NOT set to readonly even though M's config file has super_read_only=true setting, so that if we have a process which keeps connecting to M and do insert/delete/update stmts, it will succeed in this window, and gtids of such transactions is M's own server_uuid and then M can't join the MGR cluster since it has changes that the MGR cluster doesn't have.

How to repeat:
do as in description section.

Hi,

Have you tried reproducing this with 8.0.21, I was running this test whole day today and I was not able to catch this window to insert data and mess up the cluster.

Thanks
Bogdan

No feedback was provided for this bug for over a month, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".