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Profiling
To make it easier to track down performance problems GitLab comes with a set of profiling tools, some of these are available by default while others need to be explicitly enabled.
Profiling a URL
There is a Gitlab::Profiler.profile method, and corresponding
bin/profile-url script, that enable profiling a GET or POST request to a
specific URL, either as an anonymous user (the default) or as a specific user.
When using the script, command-line documentation is available by passing no arguments.
When using the method in an interactive console session, any changes to the application code within that console session will be reflected in the profiler output.
For example:
Gitlab::Profiler.profile('/my-user')
# Returns a RubyProf::Profile for the regular operation of this request
class UsersController; def show; sleep 100; end; end
Gitlab::Profiler.profile('/my-user')
# Returns a RubyProf::Profile where 100 seconds is spent in UsersController#show
Passing a logger: keyword argument to Gitlab::Profiler.profile will send
ActiveRecord and ActionController log output to that logger. Further options are
documented with the method source.
GitLab-Profiler is a project that builds on this to add some additional niceties, such as allowing configuration with a single Yaml file for multiple URLs, and uploading of the profile and log output to S3.
For GitLab.com, you can find the latest results here: http://redash.gitlab.com/dashboard/gitlab-profiler-statistics
Sherlock
Sherlock is a custom profiling tool built into GitLab. Sherlock is only
available when running GitLab in development mode and when setting the
environment variable ENABLE_SHERLOCK to a non empty value. For example:
ENABLE_SHERLOCK=1 bundle exec rails s
Recorded transactions can be found by navigating to /sherlock/transactions.
Bullet
Bullet is a Gem that can be used to track down N+1 query problems. Because
Bullet adds quite a bit of logging noise it's disabled by default. To enable
Bullet, set the environment variable ENABLE_BULLET to a non-empty value before
starting GitLab. For example:
ENABLE_BULLET=true bundle exec rails s
Bullet will log query problems to both the Rails log as well as the Chrome console.
As a follow up to finding N+1 queries with Bullet, consider writing a QueryRecoder test to prevent a regression.