I backed up a database a few weeks ago, then for comparison downloaded it again. It was about 10,000 kB larger. There should not be anyone writing to it, but there are lots of reads.
Will a static MySQL database become bigger in file size over time, even without anyone writing to it?
It's possible it could still grow, although it would be slowly if you aren't inserting and you aren't making changes. If it is being changed and you are logging changes with your recovery option, it will still grow the log. You may want to check all the jobs that touch that database as well and switch it to simple recovery if you haven't already done so.
Back in August 2014, I answered this question : How to start mysqld with read-only data directory?
I mentioned how you could make the InnoDB Architecture completely read-only.
You can also read MySQL Documentation (Configuring InnoDB for Read-Only Operation)
The only reason ibdata1 would grow would be MVCC (needed to support transaction isolation). I wrote about such uncontrolled growth of ibdata1 in my post How can Innodb ibdata1 file grows by 5X even with innodb_file_per_table set?
Turning its features removes any need to write anything related to MVCC inside ibdata1.
