InnoDB Buffer Pool contents mystery


We are using MySQL 5.044 and have the following replication topology:

1 Master and 5 Slaves

Yesterday, we added another slave machine, and set the InnoDB Buffer Pool Size to 30 GB.

This machine is not yet used by our applications, and so it is only getting INSERT/DELETE/UPDATE statements from master through replication.

Today I looked at the InnoDB Buffer Pool and I see that over 2 GB are being used already. I was surprised. I was under the impression that only data from SELECTs should go there for faster retrieval. Am I wrong? Does some data from INSERT/DELETE/UPDATE also go there, or is there something else going on?

Thank you!

InnoDB has to read the data before it changes and writes it back, and it puts it into the buffer pool when it does that.

I see …

I wonder if this is a waste of the InnoDB Buffer Pool space, as the replication related data is useless (as far as buffer usage is concerned) once it is done with whereas the data which could potentially be pushed out of the pool because of the replication related usage of the buffer could be the data which is frequently accessed.

Thank you!