Skip to content
This rails plugin not only runs "EXPLAIN" before each of your select queries in development, but provides a small DIV in the rendered output of each page with the summary of query warnings that it analyzed.
Find file
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.



QueryReviewer is an advanced SQL query analyzer. It accomplishes the following goals:

  • View all EXPLAIN output for all SELECT queries to generate a page
  • Rate a page's SQL usage into one of three categories: OK, WARNING, CRITICAL
  • Attach meaningful warnings to individual queries, and collections of queries
  • Display interactive summary on page


I use this for all my rails projects. Still the best out there in my opinion for analyzing and understanding your ActiveRecord generated queries. I forked the original query_reviewer and applied a collection of patches that have been made since the plugin was originally created. A list of additions is below:

  • Snazzed up the README into markdown for better readability
  • Fix deprecated use of require 'activesupport to active_support
  • Cleanup and move rake task to lib/tasks to fix deprecation warnings
  • Added gemspec for use with Bundler
  • Fixed missing tags and additional XHTML escaping
  • Fix sql escaping for XHTML compatibility
  • Fixes for deprecation warnings and for 1.9 compatiblity
  • Converts templates to Rails 2 + 3 friends .html.erb naming

Last commit to main repository was on March 30th, 2009. Compiled a variety of fixes that were made since that time.


All you have to do is install it! Right now this is a fork so assuming you use bundler:

# Gemfile
gem "query_reviewer", :git => "git://"

You can then run:

rake query_reviewer:setup

Which will create config/query_reviewer.yml, see below for what these options mean. If you don't create a config file, the gem will use the default in vendor/plugins/query_reviewer.


The configuration file allows you to set configuration parameters shared across all rails environment, as well as overriding those shared parameteres with environment-specific parameters (such as disabling analysis on production!)

  • enabled: whether any output or query analysis is performed. Set this false in production!
  • inject_view: controls whether the output automatically is injected before the </body> in HTML output.
  • profiling: when enabled, runs the MySQL SET PROFILING=1 for queries longer than the warn_duration_threshold / 2.0
  • production_data: whether the duration of a query should be taken into account (if you don't have real data, don't let query duration effect you!)

  • stack_trace_lines: number of lines of call stack to include in the "short" version of the stack trace

  • trace_includes_vendor: whether the "short" verison of the stack trace should include files in /vendor
  • trace_includes_lib: whether the "short" verison of the stack trace should include files in /lib

  • warn_severity: the severity of problem that merits "WARNING" status

  • critical_severity: the severity of problem that merits "CRITICAL" status

  • warn_query_count: the number of queries in a single request that merits "WARNING" status

  • critical_query_count: the number of queries in a single request that merits "CRITICAL" status

  • warn_duration_threshold: how long a query must take in seconds (float) before it's considered "WARNING"

  • critical_duration_threshold: how long a query must take in seconds (float) before it's considered "CRITICIAL"


If you disable the inject_view option, you'll need to manually put the analyzer's output into your view:

# view.html.haml
= query_review_output

and that will display the analyzer view!


Random collection of resources that might be interesting related to this utility:


There have been other alternatives created since this was originally released. A few of the best are listed below. I for one still prefer this utility over the other options:


Created by Kongregate & David Stevenson. Refactorings and compilations of all fixes since was done by Nathan Esquenazi.

Copyright (c) 2007-2008 Kongregate & David Stevenson, released under the MIT license

Something went wrong with that request. Please try again.