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MySQL Replication Slave a is lagging more and more

Hello Forum

My MySQL Replication Slave is lagging more and more and I have no clue why. This happens since last weekends application change. I see that one Core is running at 100% user time but the I/O system is nearly completely idle.

Any help is appreciated!


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Hi Oli

I assume this is a known problem related to MySQL Row Based Replication with tables on the Slave without Primary Keys.

Please check:

* If Replication is Row Based (SHOW GLOBAL VARIABLES LIKE 'binlog_format'; )
* If there are some tables on the Slave without a Primary Key
* If the currently executed event by the SQL thread is affecting one of those Primary Key less tables
* You can additionally check with SHOW GLOBAL STATUS WHERE variable_name IN ('Handler_read_rnd_next', 'Innodb_rows_read'); if there are more reads than expected. The first one is an indication of full table scans which would support my theory.

Please let us know your findings.