Rails MySQL Too Many Connections

Question

I've got a Rails 2.3 app that is keeping too many MySQL connections open. After less than a day (at ~400rpm) one process had 83 ESTABLISHED connections to the two mysql servers we use.

We're using the mysql2 gem (0.2.18), and the mysql client is: mysql Ver 14.12 Distrib 5.0.77, for redhat-linux-gnu (i686) using readline 5.1.

How can I troubleshoot where these leaks are happening? In our testing, we're never able to leak connections, its only in production.

In MySQL, we can run show processlist; to see the open connections. On the app server, we can count the number of connections per pid with sudo netstat -ntp | grep 3306 | grep ESTABLISHED | awk '{print $7}' | sort | uniq -c | sort -n.

Answer 1

I fixed this by adding "wait_timeout: 300" to our database.yml. While that does close the unused mysql connections, it doesn't explain where they came from.

Answer 2

One random idea: fork the mysql2 gem, add some debugging into Mysql2::Client#initialize, and run your app as normal. You could print a few lines of the stack when the client is initialized, and track down who's causing the leak.

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