Little bit of context before diving into the issue,
I have a Wordpress based blog running on 1 GB (RAM), 20 GB (disk space) linode instance. The database itself is around ~105 MB. Recently, I noticed that the entire disk space was used (from ~4 GB) with the database directory
/var/lib/mysql/DATABASE_NAME consuming about ~15 GB of space!
Worst offenders in this directory were files with name's ending
_INDEX_1.ibd, each one of them using ~700 MB to ~1.5 GB! A quick search didn't really return much of information about the possible cause of this issue. The database is running just fine.
In my limited experience with managing servers, I haven't really encountered something like this. It'd be great to know why this happened, possible solution and a way to prevent this from happening in future.
P.S - The database tables use InnoDB engine. And error logs are white as freshly fallen snow!