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)...
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...