MySQL 5.7 - some .IBD files 15% smaller on master than on slaves

[matthewb]

Have a look at this recent post and Yves’s answer.

Disk Divergence across Master and Slaves

So, InnoDB stores rows in b-trees. Pages in a b-tree can be anywhere between half filled (50%) and filled (100%). Let’s assume there is a long running read query running on the replica forcing a consistent read view to stay opened. A row is deleted from an innodb page and another one is later inserted to the same page. The page in question is almost full. Since there is no long running query on the master, the old rows is removed by the purge thread almost immediately and then the new row is ad…