This topic is not for all situations but in my situation it helps.
The problem is with Slave is lagging behind master in very large numbers and the relay logs are continously growing.

Slave is using:

Relay_Log_File: mysql-relay-bin.000031

But in folder where relay log resides, was created up to:

mysql-relay-bin.000135

And it is continously growing.
So what i decide to do, again step-by-step i edited my.cnf file as follows:

1. I have 13 database so give to slave paralel workers 13:
slave-parallel-workers = 13

2. Disabled sync_binlog:
sync_binlog = 0

3. Changed at_trx_commit from 1 to 0:
innodb_flush_log_at_trx_commit = 0

4. Gave log_at_timeout (only from 5.6.6>) to 10:
innodb_flush_log_at_timeout = 10

5. Disabled slow query log( or commented out)

So …

Working day to day with Percona Remote DBA customers, we have been facing an issue from time to time when MySQL replication lag is flapping between 0 and XXXXX constantly – i.e. Seconds_Behind_Master is 0 for a few secs, then it’s like 6287 or 25341, again 0 and so on. I would like to note the 5 different scenarios and symptoms of this – some are obvious and some are not really.

1. Duplicate server-ids on two or more slaves.

Symptoms: MySQL error log on a slave shows the slave thread is connecting/disconnecting from a master constantly.
Solution: check whether all nodes in the replication have unique server-ids.

2. Dual-master setup, “log_slave_updates” enabled, server-ids changed.

Scenario: you stop MySQL on the first master, then you stop the second one. …