I have an AWS RDS (MySQL 5.6.35) `db.m3.medium` that has given me a random error when attempting to modify a table's structure in the past two weeks:

`#1041 - Out of memory; check if mysqld or some other process uses all available memory; if not, you may have to use 'ulimit' to allow mysqld to use more memory or you can add more swap space`

I've never encountered this error on even a much smaller instance with much less memory. It should be noted that encryption **is** enabled on this instance, so that might be adding a little bit of load.

When I check the memory statistics in the console, it doesn't appear to be even using anywhere near 100% usage. It doesn't appear that the instance is swapping at all either. After a reboot, I can modify tables fine. This table is very small... < 10 columns, little overhead, and not many rows (<100). Oddly enough, we have not modified the default buffer sizes in RDS (3/4 of instance memory allocation). Not only this, after checking the buffer tables, everything seemed OK as well.

Am I missing something here?

UPDATE: It happened again. Rebooting the RDS server appears to mitigate whatever problem is occurring. Here's a screenshot of buffer statistics at the time of the incident (this is BEFORE the reboot that fixes the problem)... 

[![screenshot](https://i.stack.imgur.com/ORw1T.png)](https://i.stack.imgur.com/ORw1T.png)

UPDATE 9/1/2017: I thought that we mitigated the issue for a while after we upgraded our RDS instance to `m4.large`... and for a while, it did. However, while performing some migrations earlier this evening... sure enough, error #1041 - OUT OF MEMORY. I immediately checked our CloudWatch reports for anything out of the ordinary, and our freeable memory is really high, not even concerningly fluctuating. Additionally, a reboot fixed the issue. I have yet to see it happen again, but I'm sure in a few weeks after some transactions it will happen again. **Is this possibly a sign of a corrupted database or something?** We have NEVER had any issues reading or writing to the database, and all applications are using their databases on this server just fine. We just can't initiate `ALTER TABLE` changes from inside phpMyAdmin...