PQL is a query language for processes running on a system. The syntax is closely related to the one used in MongoDB. This is because at heart, PQL uses Plucky. But instead of sending the queries to a MongoDB server, they are intercepted and processed by PQL.

PQL extends the Process class with four new methods:

• find - find a process by PID
• where - find processes which match a query
• remove - remove (kill) processes
• count - count processes

These where method returns a Plucky::Query object. This object can be used to further refine the query by chaining additional methods. Consult the Plucky documentation to see which methods are available.

There is a limited number of fields which can be used in queries. The following fields are supported:

:pid, :rss, :command

The following operators are supported

gt, gte, lt, lte, in, nin

Use of an unknown field or unknown operator will raise an exception.

This will print the number of unicorn rails workers which use more than 20MB of RSS:

require 'rubygems'
require 'process-query-language'

query = Process.where(:rss.gt => 20_000_000)
query.where(:command => /unicorn_rails.worker/)
puts query.count

Copyright (c) 2010 by Tomas "wereHamster" Carnecky (tomas.carnecky@gmail.com)