AWS PostgreSQL RDS: more than 10GB increase in Freeable Storage Space without any data removed
While monitoring the metrics of my Amazon PostgreSQL RDS (db.t2.small) I noticed sudden increases in the amount of Free Storage Space. This looks rather worry some because it would imply that more 10 GB of space was removed. While checking up on the data, everything was still in place.
Has anyone encountered this before and can explain why it happens?
Postgres has a 'autovacuum' feature that is used to reclaim unused space.
All AWS RDS Postgres instances now have this featured enabled by default, so if all your data is still there, there is a good chance this is what led to more free space for you:
The autovacuum feature for PostgreSQL databases is a feature that we strongly recommend you use to maintain the health of your PostgreSQL DB instance. Autovacuum automates the execution of the VACUUM and ANALYZE command; using autovacuum is required by PostgreSQL, not imposed by Amazon RDS, and its use is critical to good performance. The feature is enabled by default for all new Amazon RDS PostgreSQL DB instances, and the related configuration parameters are appropriately set by default.
More about PostGres autovacuum:
https://www.postgresql.org/docs/9.2/static/routine-vacuuming.html