High write IOPS for MySQL instance even on low activity hours

We recently took over a wordpress project using a MySQL db instance. A few days ago, it ran out of storage causing the site to crash which we found very very strange because the db had 185GB allocated and the application isn't that big or busy to eat up all of that. We first changed the space allocated to 250 GB to allow the site to load. We then ran optimize on the tables and were able to reclaim practically all of that 250 GB and the site loaded afterwards.

We then monitored the DB and noticed that the free space was going down faster than what we are expecting and at a fairly constant rate (around 2.5 GB per 24 hours). We checked what queries are running using the show processlist command but no queries were coming up. Cron also wasn't running for the wordpress application so no background tasks there so we weren't sure what's going on.

We then realized that the write IOPS was around 150-200 when monitored through AWS and never went down even if that time was already a slow day which would contribute to the space going down. This was also probably what caused the space to run out before. We are not sure where to check next exactly. If it would help, the instance is a t3.large mysql community instance

thank you

Edited by: dogfish on Apr 26, 2020 5:14 PM

Edited by: dogfish on Apr 26, 2020 5:30 PM

Edited by: dogfish on Apr 26, 2020 5:37 PM