I'm using postgresql 9.5.4 on amazon RDS with ~1300 persistent connections from rails 4.2 with "prepared_statements: false". Over the course of hours and days, the "Freeable Memory" RDS stat continues to go down indefinitely but jumps back up to a relatively small working set every time we reconnect (restart our servers). If we let it go too long, it goes all the way to zero and the database instance really does start to go into swap and eventually fail. Subtracting the freeable memory over days from the peaks when we restart we see that there are 10's of MB per connection on average.
Digging into the per-pid RSS from enhanced monitoring, we see the same slow growth on example connection pids but the total RSS seems to just be a proxy for actual memory usage per connection (https://www.depesz.com/2012/06/09/how-much-ram-is-postgresql-using/).
How can I either:
- Change the default.postgres9.5 parameters below to avoid unbounded memory growth per-connection
- Determine what queries cause this unbounded growth and change them to prevent it
- Determine what type of buffering/caching is causing this unbounded growth so that I can use that to do either of the above