I'm running a small database in AWS RDS (t2.medium with 4G memory) and I found the freeable memory for SQL Server is only about 250MB no matter the number of connections is 20 or 200.
My database previous is running in a t2.medium EC2 without problem. I'm wondering if memory usage is more in RDS? Thanks.
freeable memory generally represents RAM of your physical server on which SQL is running. So if your freeable memory is low, then certainly it means it is getting used somewhere. If a session is performing memory intensive DDL's and DML statements then that would affect your memory and swap usage.
250mb seems too low to me given you can allow 200 connections to RDS. You should not hold your RDS too close to limits. As in case of increase in DML, DDL and TCL queries, our Ram can comsume 100% and may cause latency issues.
I would suggest you enable the slow_query_log and general_log parameters to help identify queries that could be consuming this memory. The decrease in FreeableMemory seems to be caused by the workload your instance had during the time.