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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.
rack-mini-profiler
This Gem is enabled by default in development only. It allows you to see the timings of the various components that made up a web request (e.g. the SQL queries executed and their execution timings).
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.
ActiveRecord Query Trace
This Gem adds backtraces for every ActiveRecord query in the Rails console. This
can be useful to track down where a query was executed. Because this Gem adds
quite a bit of noise (5-10 extra lines per ActiveRecord query) it's disabled by
default. To use this Gem you'll need to set ENABLE_QUERY_TRACE to a non empty
file before starting GitLab. For example:
ENABLE_QUERY_TRACE=true bundle exec rails s
rack-lineprof
This is a Gem that can trace the execution time of code on a per line basis.
Because this Gem can add quite a bit of overhead it's disabled by default. To
enable it, set the environment variable ENABLE_LINEPROF to a non-empty value.
For example:
ENABLE_LINEPROF=true bundle exec rails s
Once enabled you'll need to add a query string parameter to a request to
actually profile code execution. The name of the parameter is lineprof and
should be set to a regular expression (minus the starting/ending slash) used to
select what files to profile. To profile all files containing "foo" somewhere in
the path you'd use the following parameter:
?lineprof=foo
Or when filtering for files containing "foo" and "bar" in their path:
?lineprof=foo|bar
Once set the profiling output will be displayed in your terminal.