Thesql Replication stalled

MySQLmysql-8.0

I am having mysql 8.0 installation with replication between 2 servers in master-master configuration. While data is being replicated from server A to server B the replication is stalled from hours. Below is the snippet for show slave status \G on server B. I am not sure on what waiting for handler commit means and whether its the cause of my Replication stalling

        Master_SSL_Cipher:
       Master_SSL_Key:
Seconds_Behind_Master: 49808
        Last_IO_Errno: 0
        Last_IO_Error:
       Last_SQL_Errno: 0
       Last_SQL_Error:Replicate_Ignore_Server_Ids:
     Master_Server_Id: 1
     Master_Info_File: mysql.slave_master_info
            SQL_Delay: 0
  SQL_Remaining_Delay: NULL
  Slave_SQL_Running_State: waiting for handler commit
       Master_Retry_Count: 86400
              Master_Bind:
  Last_IO_Error_Timestamp:
 Last_SQL_Error_Timestamp:
           Master_SSL_Crl:

After executing show processlist; i am getting a process that is waiting from a long time , having a wait time of 50071 and increasing

system user     |                               | NULL | Query       | 50071 | waiting for handler commit

What steps shall i take to bring my replication on track?

Best Answer

That's new with 8.0.13:

A new Performance Schema stage, waiting for handler commit, is available to detect threads going through transaction commit. Thanks to Facebook for the patch. (Bug #27855592, Bug #90417)

https://bugs.mysql.com/bug.php?id=90417

Suggest you file a comment with that bug report; could be that it caused a regression.

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Since I see more than 2 system user entries in the processlist, I would assume you are using Multi-Threaded Replication (slave_parallel_workers > 1).

That looks like a bug

On Oct 29, 2014, this was expressed by David Moss

Thank you for your feedback. This issue was covered in bug 17326020 and the following was added to the MySQL 5.6.21 and 5.7.5 changelogs:

When the I/O thread reconnected to a master using GTIDs and multithreaded slaves while in the middle of a transaction, it failed to abort the transaction, leaving a partial transaction in the relay log, and then retrieving the same transaction again. This occurred when performing a rotation of the relay log. Now when reconnecting, the server checks before rotating the log in such cases, and waits first for any ongoing transaction to complete.

Therefore nothing new will be added to cover this bug and I'm closing it as fixed.

On Dec 10, 2014, this was expressed by Laurynas Biveinis

Problem:

With MTS, GTIDs and auto positioning enabled, when a worker applies a partial transaction left on relaylog by an IO thread reconnection, it will wait for the XID log event to commit the transaction.

Unfortunately, the SQL thread coordinator will reach the master's ROTATE event on the next relaylog file and will wait for all workers to finish their tasks before applying the ROTATE.

Analysis:

As the whole transaction is retrieved again by the IO thread after the reconnection, the slave must rollback the partial transaction once noticing this ROTATE from the master.

This bug reports the same issue already fixed by BUG#17326020, and the reported issue is not reproducible anymore. So, this patch is just adding a new test case.

SUGGESTION

Run FLUSH BINARY LOGS; on the Master

See if the movement triggers a response from the SQL threads.

If it does not, go ahead and remove slave_parallel_workers from my.cnf and restart mysql.

Since you started MySQL up and master and slave and got error 1236, that means you are trying to establish replication from an impossible position. In the context of GTID and error message you got, the binary logs needed to fully identify a set of queries within a GTID set no longer exists,

Look back at your SHOW SLAVE STATUS\G

Retrieved_Gtid_Set: 7846a847-62c7-11e5-91a6-e06995de432e:4757140-5030085
 Executed_Gtid_Set: 7846a847-62c7-11e5-91a6-e06995de432e:1-4783274

From this, the last GTID executed is 7846a847-62c7-11e5-91a6-e06995de432e:4783274

This means that the binary log that has or had 7846a847-62c7-11e5-91a6-e06995de432e:4783275 no longer exists.

I can see this happening if you stopped replication on the Slave, left replication off long enough for the Master to rotate its binary logs (via expire_logs_days) the slave still needed to see, then turned on replication.

In your particular case, try doing a mysqlbinlog dump of the binary log mysqld-bin.000141. If nothing comes out of it, you will have to reload the Slave and setup replication from scratch.

Best Answer

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