On Wed, Jun 16, 2021 at 12:02:52PM +0530, Atul Kumar wrote: > > Sometimes I run a Postgres query it takes 30 seconds. Then, I > immediately run the same query and it takes 2 seconds. It appears that > Postgres has some sort of caching. Can I somehow see what that cache > is holding? You can use pgbuffercache for that: https://www.postgresql.org/docs/current/pgbuffercache.html > Can I force all caches to be cleared for tuning purposes? > So I need to clear the cache without restarting/rebooting the postgres > server to check the correct execution plan of my query. No, cleaning postgres cache can only be done with a service restart. That being said, tuning shouldn't be done assuming that there's no cache. On the opposite maybe what you should do is use pg_prewarm (https://www.postgresql.org/docs/current/pgprewarm.html) to make sure that your cache isn't empty after a restart. Note that you also have the operating system cache. It can be cleared without restarting the OS, but I have no idea if this is possible with RDS.
