MySQL Bugs: #113503: Error in semisynch diagram

Bug #113503	Error in semisynch diagram
Submitted:	24 Dec 2023 7:38	Modified:	14 Feb 17:05
Reporter:	Pravata Dash	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Documentation	Severity:	S3 (Non-critical)
Version:	8.0	OS:	Any
Assigned to:	Jon Stephens	CPU Architecture:	Any

Description:
Link: https://dev.mysql.com/doc/refman/8.0/en/group-replication-primary-secondary-replication.ht...

Image: Figure 18.2 MySQL Semisynchronous Replication

In the official mysql GR documentation there is a section(MySQL Semisynchronous Replication), in which image its shown that the semi-sync enabled replica gives back the ack to the master after its been applied to the replica after being written to the relay log.

AFAIK, the above is not the case.

In MySQL semisynchronous replication, the semi-sync enabled replica returns an ACK to the primary after the data has been written to the relay log, but not necessarily after it has been applied. 

The steps would be:

> Transaction written on the primary
> Data sent to replica
> Replica writes to relay log
> Replica sends ACK
> Primary commits
> Replica applies events (asynchronously)

> The replica applies the events from the relay log to its database, but this happens asynchronously, without coordination with the primary.
This means there might be a slight lag between the transaction committing on the primary and being fully applied on the replica.

How to repeat:
It's a documentation issue, there is nothing to repeat here.

Suggested fix:
Link: https://dev.mysql.com/doc/refman/8.0/en/group-replication-primary-secondary-replication.ht...

Image: Figure 18.2 MySQL Semisynchronous Replication

In the official documentation pic, the image needs to be corrected, where the ACK from the semi-sync enabled replica needs to be sent back from relaylog block, not the apply block.

Please let me know in case my understanding is wrong here.

Image having issue with

Attachment: Screenshot 2023-12-24 at 1.09.12 PM.png (image/png, text), 186.80 KiB.

Hello Pravata Dash,

Thank you for the report and feedback.

regards,
Umesh

Are we planning to fix the image in the official link?

Hi Pravata,

Yes, the bug status is Verified, which means we acknowledge that it needs to be fixed.

It's been assigned to me for resolution; I'll have to put in a request to Graphics to get the image updated; I don't know how long this will take.

We'll update the status of the bug when this has been done.

Thanks!

jon.

Thanks for the confirmation.