counters

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h1. Counters

Easily record any metrics from anywhere within your code, using a very simple interface:

• ping: When's the last time we saw this thing?
• hit: Increments a counter
• magnitude: Measures numerical values
• latency: Measures time intervals

h2. Example

Let's say you have a web crawler. There are a ton of things you can measure about your crawler: how many pages it processed (#hit), how many bytes you read (#magnitude), how long did it take to download the page (#latency), how long did it take to parse the raw HTML to a useable format (#latency).

require "uri"
require "open-uri"
require "counters"
require "nokogiri"

Counter = Counters::Redis.new(Redis.new, :namespace => "crawler", :base_key => "counters")

urls_to_crawl = ["http://blog.teksol.info/", "http://techcrunch.com/", "http://www.google.com/"]

while url = urls_to_crawl.pop
  Counter.ping "crawler"

  begin
    Counter.hit "urls_popped"

    puts "Fetching #{url}"
    raw_html = Counter.latency "download" do
      URI.parse(url).read
    end

    Counter.magnitude "bytes_in", raw_html.length

    parsed_html = Counter.latency "html_parsing" do
      Nokogiri::HTML(raw_html)
    end
  rescue
    Counter.hit "error"
  end
end

h2. Other Backends

For testing purposes, there also exists a Counters::Memory. This would be good in test mode, for example. The counters are exposed through accessor methods returning a Hash.

You may log to a file, but be advised the file's size grows very quickly. Counters are stored in the file, one per line, in an easily readable format.

$ irb -r counters
> Counter = Counters::File.new("counters.log")
 => #<:file:0x00000101a18f18>, @formatter=#<0x00000101a18bd0><:logdevice:0x00000101a18e28><:logdevice::logdevicemutex:0x00000101a18e00>

""

""