InnoDB file release after delete

[Alexandru Badulescu]

Hi,
We're usinng Mysql 5.7, and the normal database location is on the server's SSD drive. We have daily data in separate tables (1 table per day).
Since the SSD is only 1 TB, we need to move older data to a RAID storage. What we normally do is to move the appropriate idb and frm files and create soft-links for them in the database dir.
The problem is that the MySQL process seem to keep some files open, so the space is not freed up. On slave machines we can solve this by restarting MyQL, but on the master server we have to avoid restarts...
Is there a way to force MySQL to release those files?
Is there a way to know how long would it keep such a a file open? (there were no recent queries on those tables, and some were still open after weeks).

Would you propose any other solution to avoid this problem?


Thanks,
Alex