MySQL Replication – Is `log_bin` Necessary on Slave?

MySQLmysql-5.7replication

I'm running out of disk space on a slave due to MySQL binary logs (mysql-bin.000xxx) being stored on the slave.

Here's the relevant portion of the slave's my.cnf:

binlog_format  = mixed
log_bin        = /var/log/mysql/mysql-bin.log
sync_binlog    = 1

I'm currently catching up to Master, so I expect to see a bunch of mysql-relay-bin.00xxxx's on Slave, but I'm not sure why it also needs mysql-bin.000xxx's.

The Master also has a lot of mysql-bin.000xxx's, but I expect it there.

Best Answer

If the slave is not a master to other slaves, then you do not need binary logging on the slave

To reclaim the space of those logs on the Slave immediately, run this

mysql> STOP SLAVE;
mysql> RESET MASTER;
mysql> START SLAVE;

This will hose all binary logs on the Slave.

You could then remove or comment out log_bin from the my.cnf of the Slave and restart mysqld

Related Solutions

Mysql – Will thesql_secure_install script block master updates to slave

If by disable remote login you mean it added skip-networking, you'll want to remove that from your my.cnf and restart mysql

MySQL – Master Binlog Corruption

Surprisingly, that's not gibberish.

That indeed appears at the top of binlogs whenever you do mysqlbinlog to a binary log generated using MySQL 5.1 and MySQL 5.5. You will not see that gibberish in binary logs for MySQL 5.0 and back.

This is why the start point for replication from an empty binary log is

107 for MySQL 5.5
106 for MySQL 5.1
98 for MySQL 5.0 and back

This is good to remember if you do MySQL Replication where the Master if MySQL 5.1 and the slave is MySQL 5.0. This could present a really big headache.

Replication from Master using 5.0 and Slave using 5.1 works fine, not the other way around.(According to MySQL Documentation, it is generally not supported for 3 reasons: 1) Binary Log Format, 2) Row-based Replication, 3) SQL Incompatibility).

Anyway, do a mysqlbinlog on the offending binary log on the master. If the resulting dump produces gibberish in the middle of the dump (which I have seen a couple of times in my DBA career) you may have to skip to position 98 (MySQL 5.0) or 106 (MySQL 5.1) or 107 (MySQL 5.5) of the master's next binary log and start replicating from there (SOB :( you may need to use MAATKIT tools mk-table-checksum and mk-table-sync to reload master changes not on the slave [if you want to be a hero]; even worse, mysqldump the master and reload the slave and start replication totally over [if you don't want to be a hero])

If the mysqlbinlog of the master is completely readable after the top gibberish you saw, it is possible the master's binary log is fine but the relay log on the slave is corrupt (due to transmission/CRC errors). If that's the case, just reload the relay logs by issuing the CHANGE MASTER TO command as follows:

STOP SLAVE;
CHANGE MASTER TO
MASTER_HOST='< master-host ip or DNS >',
MASTER_PORT=3306,
MASTER_USER='< usernmae >',
MASTER_PASSWORD='< password >',
MASTER_LOG_FILE='< MMMM >',
MASTER_LOG_POS=< PPPP >;
START SLAVE;

Where

MMMM is the last file used from the Master that was last processed on the Slave
PPPP is the last position used from the Master that was last processed on the Slave

You can get MMMM and PPPP by doing SHOW SLAVE STATUS\G and using

Relay_Master_Log_File for MMMM
Exec_Master_Log_Pos for PPPP

Try it out and let me know !!!

BTW running CHANGE MASTER TO command erases the slave's current relay logs and starts fresh.

Best Answer

Related Solutions

Mysql – Will thesql_secure_install script block master updates to slave

MySQL – Master Binlog Corruption

Related Question