Module: ActionController

Defined in:

lib/custom_benchmarks.rb

Overview

Custom Benchmarks

Custom Benchmarks allow you to easily log your own information to the rails log at the end of each request. The standard rails summary log line looks like this:

Completed in 5ms (View: 3, DB: 2) | 200 OK [zvm/]

With custom_benchmarks, an additional line is added to the output that contains as many metrics as you like for each request. e.g.,

Completed in 5ms (View: 3, DB: 2) | 200 OK [zvm/] Finished WelcomeController#index in 0.08545 (11 reqs/sec) DB: 2 | PID: 30796 | Time: 1233202720 | 200 OK [zvm/]

Typically, the log line includes the latency associated with executing specific parts of a request. In the example above, we have added a measurement of search latency. But you can use Custom Benchmarks to add any information to the log line. The example above also shows the ID of the process (PID) that served this request. The PID is useful when parsing information from logs that contain data from multiple processes.

Simple Example: Logging the Process ID

To add the PID as a custom benchmark field, simply add a custom_benchmark line like the following to your ApplicationController:

class ApplicationController < ActionController::Base

custom_benchmark {|runtime| " | PID: #{$$}" }
...

end

Declare your custom_benchmark with a block that expects an input parameter called runtime. runtime, which isn’t used in this example, contains the overall latency of the entire request. Later, we’ll show you an example of using runtime to calculate percentage latency below. custom_benchmark expects your block to return a string - which will be inserted in the log file immediate before the status (e.g., 200 OK [www.zvents.com/])

Complex Example: Logging Arbitrary Latency

Let’s say that your application includes a search function that is powered by Lucene. Like SQL calls issued to a database, calls to Lucene can take a while so you want to log your search latency.

The first step is to set up a mechanism that allows you to record your search latency for each request. You can do that with something like this:

class MySearch

@@latency = 0.0
cattr_accessor :latency

def run_search
  @@latency = Benchmark::measure{
    # execute the call to Lucene here
  }.real
end

def self.get_timing_summary(runtime)
  summary = " | Search: #{sprintf("%.5f",@@latency)} (#{sprintf("%d", (@@latency * 100) / runtime)}%)"
  @@latency = 0.0
  summary
end

end

The run_search method uses Benchmark::measure to record the latency of the search. The get_timing_summary class method, which will be invoked by a custom_benchmark, returns a formatted string summarizing the search latency in absolute and percentage terms. It also resets the value of @@latency to avoid affecting subsequent queries.

Finally, we just need to add a custom_benchmark statement to the ApplicationController:

custom_benchmark {|runtime| MySearch.get_timing_summary(runtime) }

Defined Under Namespace

Modules: CustomBenchmarking