MySQL Slave database size >> Master Database I have a Percona MySQL Master-Master setup (5.6) with second master as passive master(read-only).

Slave:

mysql&gt; SELECT table_schema AS "Database", ROUND(SUM(data_length + index_length) / 1024 / 1024, 2) AS "Size (MB)" FROM information_schema.TABLES GROUP BY table_schema;
+--------------------+-----------+
| Database           | Size (MB) |
+--------------------+-----------+
| common_schema      |      1.89 |
| information_schema |      0.01 |
| mysql              |      1.70 |
| dataplay           |   1684.56 |
| dataplay1          |      0.14 |
| percona            |      0.20 |
| performance_schema |      0.00 |
+--------------------+-----------+


Master:

mysql&gt; SELECT table_schema AS "Database", ROUND(SUM(data_length + index_length) / 1024 / 1024, 2) AS "Size (MB)" FROM information_schema.TABLES GROUP BY table_schema;
+--------------------+-----------+
| Database           | Size (MB) |
+--------------------+-----------+
| common_schema      |      1.89 |
| information_schema |      0.01 |
| mysql              |      1.69 |
| dataplay           |   1614.80 |
| dataplay1          |      0.14 |
| percona            |      0.20 |
| performance_schema |      0.00 |
+--------------------+-----------+
7 rows in set (0.07 sec)


The size difference is massive. Is it something wrong with the setup which is running? What is wrong?
From the details, it looks like the 'massive' difference is ~70MB in the dataplay schema. You can adjust your query to find out exactly which tables are different.

Two potential reasons for this difference is:


Schema difference on the master vs slave. Does the slave have utf8 instead of latin1 on a column or three? Does the slave have additional indexes? You can compare the schema by running a mysqldump of just the schema (--no-data option) and then diff'ing the results.
The slave has actual different data. Do you have session-only data that the application stores and won't matter? If no, you can use pt-table-checksum to find rows that are actually different. Then you need to dig into why they are different and fix that issue before reseeding the passive master or using pt-table-sync to resolve the differences.