MySQL Bugs: #110127: semi-sync master wait for ack when semi-sync replica is down & async replaces it

Bug #110127	semi-sync master wait for ack when semi-sync replica is down & async replaces it
Submitted:	19 Feb 2023 11:37	Modified:	22 Feb 2023 20:20
Reporter:	Yunus Shaikh	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Replication	Severity:	S3 (Non-critical)
Version:	8.0.31	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	MySQL, Semi-sync replication

Description:
The below scenario works fine in 8.0.29 and 8.0.30 but does not work in 8.0.31

1) Semi-sync master is replicating to one semi-sync replica and async replica
2) semi-sync replica goes down
3) rpl_semi_sync_source_timeout is set to a high value for not letting transactions go ahead without acknowledgement from at least one replica.
4) Master waits for ack from semi-sync replica but semi-sync replica is down.
5) Enable semi-sync on the async replica. Restart replica.

This should allow master to move ahead because the acknowledgement is received on the new semi-sync replica but it does not move ahead in 8.0.31.
While it works fine in older version.

How to repeat:
Step 1 -
dbdeployer deploy replication --nodes=3 --topology=master-slave --gtid --semi-sync --read-only-slaves 8.0.31 --force --port 5800

Step 2 -
Stop node1
./node1/stop

Step 3 -
Set Node 3 as async replica
set global rpl_semi_sync_slave_enabled = OFF;
stop replica; start replica;

Step 4 -
connect to master and try to run some transaction after increasing timeout to large value

set global rpl_semi_sync_master_timeout = 36000000;
create database test1;

Step 5 -
Connect to replica2 and enable semi-sync on it.
set global rpl_semi_sync_slave_enabled=ON;
stop replica;start replica;

Result -
Master still waits when async replica is converted to semi-sync.
Master wait for transaction with status Waiting for semi-sync ACK from slave

Expected -
When async replica is converted into semi-sync replica, master should start processing the transactions when rpl_semi_sync_source_wait_for_replica_count = 1. Because the semi-sync replica will acknowledge the transaction.

Expected - Master

Hi,

Thank you for the report, verified as descibed

This is a regression from https://github.com/mysql/mysql-server/commit/650d2f7bf275e40fd605df39ab09949aa54f5e3f

--
Venkatesh

Contribution patch based on 8.0.34 code to fix the issue (*) I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: 0001-Bug-110127-semi-sync-master-wait-for-ack-when-semi-s.patch (text/x-patch), 11.21 KiB.

Contribution submitted via Github - Bug#110127: semi-sync master wait for ack when semi-sync replica is down & async (*) Contribution by Venkatesh Prasad Venugopal (Github venkatesh-prasad-v, mysql-server/pull/490#issuecomment-1682441126): I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: git_patch_1479206153.txt (text/plain), 11.21 KiB.

Hi Umesh,

Any updates on this?

--
Venkatesh Prasad (Venu)