20% CPU usage by RDS instance when idle

Question

I have brought up a db.t1.micro PostgreSQL instance in us-east-1 region.

1. It's single availability zone
2. no backups
3. not in a security group that's reachable from the outside world

For some reason the CPU usage is at 20% CPU while I'm doing absolutely nothing, exactly every 10 minutes spiking to 28-30%. I thought there was something wrong with the instance, so I've re-created it, same thing.

What does this? Is this an RDS phenomenon in general or is this specific to the burst capable instance classes?

Answer 1

This seems to be a common problem of t1.* or t2.* instances which is acknowledged by AWS support but not resolved yet. Some users are trying to mitigate the issue by restarting the instance with CloudWatch custom alarm monitoring CPU usage. I wouldn't recommend it as this is a temporary solution for RDS Multi-AZ deployments only and CPU spikes will reappear again what I have read so far.

If you are really sure that there are no queries running during the CPU spike periods which could cause them and that other related CloudWatch metrics are fine I would definitely contact AWS support.

Here it is how you can find out running queries:

SELECT * FROM pg_stat_activity;
SELECT pid, datname, usename, query FROM pg_stat_activity;

Here are CloudWatch metrics to check:

read/write IOPS
read/write latency
network throughput
binary log disk usage
freeable memory
queue depth

Further information can be found on AWS forums:

https://forums.aws.amazon.com/thread.jspa?threadID=164532

https://forums.aws.amazon.com/thread.jspa?threadID=169893