Master – 192.168.56.3

Slave – 192.168.56.4

Percona Toolkit Version – 3.0.12

MySQL Version -MySQL GA 5.7.23

I have created a user in the master to check and repair:

GRANT ALL ON *.* to chksum@'%' identified by 'Password@2018';

In case you have non default ports (3306) for MySQL, Please set the following variables on the slaves:

# my.cnf
[mysqld]
report_host = slave
report_port = 3307

Confirm data inconsistencies in Master (192.168.56.3) and Slave (192.168.56.4):

Master

mysql> select count(1) from titles; 
+----------+
| count(1) |
+----------+
|   443308 |
+----------+
1 row in set (0.09 sec)

Slave

mysql> select count(1) from titles; 
+----------+
| count(1) |
+----------+
|   443311 |
+----------+
1 row in set (0.09 sec)

Check data inconsistencies using pt-table-checksum:

Check for data inconsistencies by executing the following command** on the Master:

** command I have executed below :- pt-table-checksum h=192.168.56.3,u=chksum,p=Password@2018,P=3306 –set-vars innodb_lock_wait_timeout=30 –no-check-binlog-format –databases=employees –tables=titles

[root@localhost ~]# pt-table-checksum h=192.168.56.3,u=chksum,p=Password@2018,P=3306 --set-vars innodb_lock_wait_timeout=30 --no-check-binlog-format --databases=employees --tables=titles
Checking if all tables can be checksummed ...
Starting checksum ...
            TS ERRORS  DIFFS     ROWS  DIFF_ROWS  CHUNKS SKIPPED    TIME TABLE
09-20T22:53:02      0      2   443308          5       6       0   1.319 employees.titles

Fixing data inconsistencies using pt-table-checksum

We are checking data inconsistency from Master (192.168.56.3) to Slave (192.168.56.3) by executing the following command** on the Master:

** command I have executed below :- pt-table-sync –sync-to-master h=192.168.56.4,u=chksum,p=Password@2018,P=3306 –databases=employees –tables=titles –print

[root@localhost ~]# pt-table-sync --sync-to-master h=192.168.56.4,u=chksum,p=Password@2018,P=3306 --databases=employees --tables=titles --print
REPLACE INTO `employees`.`titles`(`emp_no`, `title`, `from_date`, `to_date`) VALUES ('10144', 'Senior Staff', '1992-10-14', '1993-08-10') /*percona-toolkit src_db:employees src_tbl:titles src_dsn:P=3306,h=192.168.56.3,p=...,u=chksum dst_db:employees dst_tbl:titles dst_dsn:P=3306,h=192.168.56.4,p=...,u=chksum lock:1 transaction:1 changing_src:1 replicate:0 bidirectional:0 pid:3789 user:root host:localhost.localdomain*/;
REPLACE INTO `employees`.`titles`(`emp_no`, `title`, `from_date`, `to_date`) VALUES ('10144', 'Staff', '1985-10-14', '1992-10-14') /*percona-toolkit src_db:employees src_tbl:titles src_dsn:P=3306,h=192.168.56.3,p=...,u=chksum dst_db:employees dst_tbl:titles dst_dsn:P=3306,h=192.168.56.4,p=...,u=chksum lock:1 transaction:1 changing_src:1 replicate:0 bidirectional:0 pid:3789 user:root host:localhost.localdomain*/;
DELETE FROM `employees`.`titles` WHERE `emp_no`='87000' AND `title`='Staff Engineer' AND `from_date`='1990-01-01' LIMIT 1 /*percona-toolkit src_db:employees src_tbl:titles src_dsn:P=3306,h=192.168.56.3,p=...,u=chksum dst_db:employees dst_tbl:titles dst_dsn:P=3306,h=192.168.56.4,p=...,u=chksum lock:1 transaction:1 changing_src:1 replicate:0 bidirectional:0 pid:3789 user:root host:localhost.localdomain*/;
DELETE FROM `employees`.`titles` WHERE `emp_no`='97000' AND `title`='Database Engineer' AND `from_date`='1991-01-01' LIMIT 1 /*percona-toolkit src_db:employees src_tbl:titles src_dsn:P=3306,h=192.168.56.3,p=...,u=chksum dst_db:employees dst_tbl:titles dst_dsn:P=3306,h=192.168.56.4,p=...,u=chksum lock:1 transaction:1 changing_src:1 replicate:0 bidirectional:0 pid:3789 user:root host:localhost.localdomain*/;
DELETE FROM `employees`.`titles` WHERE `emp_no`='97500' AND `title`='Project Manager' AND `from_date`='1983-04-11' LIMIT 1 /*percona-toolkit src_db:employees src_tbl:titles src_dsn:P=3306,h=192.168.56.3,p=...,u=chksum dst_db:employees dst_tbl:titles dst_dsn:P=3306,h=192.168.56.4,p=...,u=chksum lock:1 transaction:1 changing_src:1 replicate:0 bidirectional:0 pid:3789 user:root host:localhost.localdomain*/;
DELETE FROM `employees`.`titles` WHERE `emp_no`='97501' AND `title`='Project Manager' AND `from_date`='1983-04-11' LIMIT 1 /*percona-toolkit src_db:employees src_tbl:titles src_dsn:P=3306,h=192.168.56.3,p=...,u=chksum dst_db:employees dst_tbl:titles dst_dsn:P=3306,h=192.168.56.4,p=...,u=chksum lock:1 transaction:1 changing_src:1 replicate:0 bidirectional:0 pid:3789 user:root host:localhost.localdomain*/;
DELETE FROM `employees`.`titles` WHERE `emp_no`='97502' AND `title`='Project Engineer' AND `from_date`='1993-04-11' LIMIT 1 /*percona-toolkit src_db:employees src_tbl:titles src_dsn:P=3306,h=192.168.56.3,p=...,u=chksum dst_db:employees dst_tbl:titles dst_dsn:P=3306,h=192.168.56.4,p=...,u=chksum lock:1 transaction:1 changing_src:1 replicate:0 bidirectional:0 pid:3789 user:root host:localhost.localdomain*/;
[root@localhost ~]# 

To fix inconsistencies on MySQL Master against the Slave execute the following command on the Master:

[root@localhost ~]# pt-table-sync --sync-to-master h=192.168.56.4,u=chksum,p=Password@2018,P=3306 --databases=employees --tables=titles --execute

Confirm the data inconsistencies in Master (192.168.56.3) and Slave (192.168.56.4) are fixed:

Master

mysql> select count(1) from titles;
+----------+
| count(1) |
+----------+
|   443308 |
+----------+
1 row in set (0.09 sec)

Slave

mysql> select count(1) from titles;
+----------+
| count(1) |
+----------+
|   443308 |
+----------+
1 row in set (0.09 sec)

Conclusion 

I recommend / encourage my customers to perform pt-table-checksum exercise regularly in their MySQL replication infrastructure to avoid unpleasant experiences due to data consistency issues.

The post How to check and fix MySQL replication inconsistencies ? appeared first on The WebScale Database Infrastructure Operations Experts.