502 Proxy Error with Apache, Node, and MySQL

gistfile1.txt

Setup:
  Node running on :8080
	Apache running on :80
	Using Apache mod_proxy to forward application requests to :8080

Symptoms 

On client:
	1. Proxy Error
		The proxy server received an invalid response from an upstream server.
		The proxy server could not handle the request GET /route.

		Reason: Error reading from remote server

		(with 502 header)

	2. Hanging page load (request sends, no response received)
	3. Routes without complex/any queries work fine after restarting Node

In Apache error_log:
	1. [error] [client xx.xx.xxx.10] proxy: Error reading from remote server returned by /route
	2. [error] [client xx.xx.xxx.10] (70014)End of file found: proxy: error reading status line from remote server localhost:8080

In Node error log:
	1. Nothing

On server:
	1. Simple SELECT queries on database work fine
	2. Complex queries hang indefinitely
	3. Running "SHOW PROCESSLIST" produces a list of queries with the status "Waiting for table-level lock"


Temporary fix
	1. In MySQL, run "SHOW PROCESSLIST"
	2. For each process, run "KILL [unique id]"
        3. Restart Apache
        4. Restart Node
        After doing this, CPU usage dropped from ~12% to ~0.5% and performance went back to normal

A slightly better fix
        1. Bash script to kill all at once per this answer: http://serverfault.com/questions/11357/bulk-or-mass-killing-misbehaving-mysql-queries

Ideal fix
        1. Figure out what is causing certain queries to obtain the status of "Waiting for table-level lock". Could have something to do with the database storage engine being InnoDB instead of MyISAM (http://stackoverflow.com/questions/6543624/what-is-waiting-for-table-level-lock)