til/rails/clean-up-memory-hungry-rails-console-processes.md

Clean Up Memory Hungry Rails Console Processes

I noticed (using htop) that a remote server hosting a Rails app had most of its RAM being actively consumed. This was hindering my ability to run a fresh deploy because the deploy processes had to do a ton of memory swapping which drastically slowed the whole thing down.

With some investigation, I discovered that most of the memory was being consumed by a handful of rails console processes. I didn't have any known active rails console processes that I was using. That combined with the dates of these processes starting way in the past suggested to me that these were abandoned processes that hadn't been properly cleaned up.

server:~# ps aux | grep rails
32767     878915  0.0  0.0 1227160  936 pts/0    Ssl+  2025   0:03 /exec rails console
32767     878942  0.9  6.5 830996 261748 pts/0   Rl+   2025 249:51 ruby /app/bin/rails console
32767    3004097  0.0  0.0 1227160  692 pts/0    Ssl+  2025   0:04 /exec rails console
32767    3004129  0.9  6.4 834672 257228 pts/0   Dl+   2025 406:31 ruby /app/bin/rails console
32767    3048582  0.0  0.0 1227160  940 pts/0    Ssl+ Jan09   0:00 /exec rails console
32767    3048611  1.1  6.3 829936 253484 pts/0   Dl+  Jan09  60:50 ruby /app/bin/rails console
32767    3060033  0.0  0.0 1227160  944 pts/0    Ssl+  2025   0:04 /exec rails console
32767    3060063  0.9  6.5 838084 260812 pts/0   Rl+   2025 405:37 ruby /app/bin/rails console
root     3699372  0.0  0.0   7008  1300 pts/0    S+   15:51   0:00 grep --color=auto rails
server:~# ps aux | grep 'rails console' | awk '{sum+=$6} END {print sum/1024 " MB"}'
1014.64 MB

As we can see by tacking on this awk command, these processes are consuming 1GB of memory.

Each of these is a pair of processes. A parent process (/exec rails console) that kicks off and supervises the memory-hungry child process (ruby /app/bin/rails console).

To free up this memory, I targeted each of the parent processes with a kill command one by one. For example:

server:~# kill 878915

I suspect that I may have left the occasional terminal tab open with one of these rails console processes running and the SSH connection was getting killed without the rails console getting killed with it.