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| stage | group | info |
|---|---|---|
| none | unassigned | To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/product/ux/technical-writing/#assignments |
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.
The first argument to the profiler is either a full URL (including the instance hostname) or an absolute path, including the leading slash.
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 is 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
For routes that require authorization you must provide a user to
Gitlab::Profiler. You can do this like so:
Gitlab::Profiler.profile('/gitlab-org/gitlab-test', user: User.first)
Passing a logger: keyword argument to Gitlab::Profiler.profile sends
ActiveRecord and ActionController log output to that logger. Further options are
documented with the method source.
Gitlab::Profiler.profile('/gitlab-org/gitlab-test', user: User.first, logger: Logger.new($stdout))
There is also a RubyProf printer available:
Gitlab::Profiler::TotalTimeFlatPrinter. This acts like
RubyProf::FlatPrinter, but its min_percent option works on the method's
total time, not its self time. (This is because we often spend most of our time
in library code, but this comes from calls in our application.) It also offers a
max_percent option to help filter out outer calls that aren't useful (like
ActionDispatch::Integration::Session#process).
There is a convenience method for using this,
Gitlab::Profiler.print_by_total_time:
result = Gitlab::Profiler.profile('/my-user')
Gitlab::Profiler.print_by_total_time(result, max_percent: 60, min_percent: 2)
# Measure Mode: wall_time
# Thread ID: 70005223698240
# Fiber ID: 70004894952580
# Total: 1.768912
# Sort by: total_time
#
# %self total self wait child calls name
# 0.00 1.017 0.000 0.000 1.017 14 *ActionView::Helpers::RenderingHelper#render
# 0.00 1.017 0.000 0.000 1.017 14 *ActionView::Renderer#render_partial
# 0.00 1.017 0.000 0.000 1.017 14 *ActionView::PartialRenderer#render
# 0.00 1.007 0.000 0.000 1.007 14 *ActionView::PartialRenderer#render_partial
# 0.00 0.930 0.000 0.000 0.930 14 Hamlit::TemplateHandler#call
# 0.00 0.928 0.000 0.000 0.928 14 Temple::Engine#call
# 0.02 0.865 0.000 0.000 0.864 638 *Enumerable#inject
To print the profile in HTML format, use the following example:
result = Gitlab::Profiler.profile('/my-user')
printer = RubyProf::CallStackPrinter.new(result)
printer.print(File.open('/tmp/profile.html', 'w'))
Stackprof support
By default, Gitlab::Profiler.profile uses a tracing profiler called ruby-prof. However, sampling profilers
run faster and use less memory, so they might be preferred.
You can switch to Stackprof (a sampling profiler) to generate a profile by passing sampling_mode: true.
Pass in a profiler_options hash to configure the output file (out) of the sampling data. For example:
Gitlab::Profiler.profile('/gitlab-org/gitlab-test', user: User.first, sampling_mode: true, profiler_options: { out: 'tmp/profile.dump' })
You can get a summary of where time was spent by running Stackprof against the sampling data. For example:
stackprof tmp/profile.dump
Example sampling data:
==================================
Mode: wall(1000)
Samples: 8745 (6.92% miss rate)
GC: 1399 (16.00%)
==================================
TOTAL (pct) SAMPLES (pct) FRAME
1022 (11.7%) 1022 (11.7%) Sprockets::PathUtils#stat
957 (10.9%) 957 (10.9%) (marking)
493 (5.6%) 493 (5.6%) Sprockets::PathUtils#entries
576 (6.6%) 471 (5.4%) Mustermann::AST::Translator#decorator_for
439 (5.0%) 439 (5.0%) (sweeping)
630 (7.2%) 241 (2.8%) Sprockets::Cache::FileStore#get
208 (2.4%) 208 (2.4%) ActiveSupport::FileUpdateChecker#watched
206 (2.4%) 206 (2.4%) Digest::Instance#file
544 (6.2%) 176 (2.0%) Sprockets::Cache::FileStore#safe_open
176 (2.0%) 176 (2.0%) ActiveSupport::FileUpdateChecker#max_mtime
268 (3.1%) 147 (1.7%) ActiveRecord::ConnectionAdapters::PostgreSQLAdapter#exec_no_cache
140 (1.6%) 140 (1.6%) ActiveSupport::BacktraceCleaner#add_gem_filter
116 (1.3%) 116 (1.3%) Bootsnap::CompileCache::ISeq.storage_to_output
160 (1.8%) 113 (1.3%) Gem::Version#<=>
109 (1.2%) 109 (1.2%) block in <main>
108 (1.2%) 108 (1.2%) Gem::Version.new
131 (1.5%) 105 (1.2%) Sprockets::EncodingUtils#unmarshaled_deflated
1166 (13.3%) 82 (0.9%) Mustermann::RegexpBased#initialize
82 (0.9%) 78 (0.9%) FileUtils.touch
72 (0.8%) 72 (0.8%) Sprockets::Manifest.compile_match_filter
71 (0.8%) 70 (0.8%) Grape::Router#compile!
91 (1.0%) 65 (0.7%) ActiveRecord::ConnectionAdapters::PostgreSQL::DatabaseStatements#query
93 (1.1%) 64 (0.7%) ActionDispatch::Journey::Path::Pattern::AnchoredRegexp#accept
59 (0.7%) 59 (0.7%) Mustermann::AST::Translator.dispatch_table
62 (0.7%) 59 (0.7%) Rails::BacktraceCleaner#initialize
2492 (28.5%) 49 (0.6%) Sprockets::PathUtils#stat_directory
242 (2.8%) 49 (0.6%) Gitlab::Instrumentation::RedisBase.add_call_details
47 (0.5%) 47 (0.5%) URI::RFC2396_Parser#escape
46 (0.5%) 46 (0.5%) #<Class:0x00000001090c2e70>#__setobj__
44 (0.5%) 44 (0.5%) Sprockets::Base#normalize_logical_path
You can also generate flamegraphs:
stackprof --d3-flamegraph tmp/profile.dump > flamegraph.html
See the Stackprof documentation for more details.
Speedscope flamegraphs
You can generate a flamegraph for a particular URL by selecting a flamegraph sampling mode button in the performance bar or by adding the performance_bar=flamegraph parameter to the request.
Find more information about the views in the Speedscope docs.
Find more information about different sampling modes in the Stackprof docs.
This is enabled for all users that can access the performance bar.
Bullet
Bullet is a Gem that can be used to track down N+1 query problems. Bullet section is displayed on the performance-bar.
Because Bullet adds quite a bit of logging noise the logging is disabled by default.
To enable the logging, set the environment variable ENABLE_BULLET to a non-empty value before
starting GitLab. For example:
ENABLE_BULLET=true bundle exec rails s
Bullet logs query problems to both the Rails log as well as the browser console.
As a follow up to finding N+1 queries with Bullet, consider writing a QueryRecoder test to prevent a regression.
System stats
During or after profiling, you may want to get detailed information about the Ruby virtual machine process, such as memory consumption, time spent on CPU, or garbage collector statistics. These are easy to produce individually through various tools, but for convenience, a summary endpoint has been added that exports this data as a JSON payload:
curl localhost:3000/-/metrics/system | jq
Example output:
{
"version": "ruby 2.7.2p137 (2020-10-01 revision a8323b79eb) [x86_64-linux-gnu]",
"gc_stat": {
"count": 118,
"heap_allocated_pages": 11503,
"heap_sorted_length": 11503,
"heap_allocatable_pages": 0,
"heap_available_slots": 4688580,
"heap_live_slots": 3451712,
"heap_free_slots": 1236868,
"heap_final_slots": 0,
"heap_marked_slots": 3451450,
"heap_eden_pages": 11503,
"heap_tomb_pages": 0,
"total_allocated_pages": 11503,
"total_freed_pages": 0,
"total_allocated_objects": 32679478,
"total_freed_objects": 29227766,
"malloc_increase_bytes": 84760,
"malloc_increase_bytes_limit": 32883343,
"minor_gc_count": 88,
"major_gc_count": 30,
"compact_count": 0,
"remembered_wb_unprotected_objects": 114228,
"remembered_wb_unprotected_objects_limit": 228456,
"old_objects": 3185330,
"old_objects_limit": 6370660,
"oldmalloc_increase_bytes": 21838024,
"oldmalloc_increase_bytes_limit": 119181499
},
"memory_rss": 1326501888,
"memory_uss": 1048563712,
"memory_pss": 1139554304,
"time_cputime": 82.885264633,
"time_realtime": 1610459445.5579069,
"time_monotonic": 24001.23145713,
"worker_id": "puma_0"
}
NOTE: This endpoint is only available for Rails web workers. Sidekiq workers can not be inspected this way.
Settings that impact performance
Application settings
developmentenvironment by default works with hot-reloading enabled, this makes Rails to check file changes every request, and create a potential contention lock, as hot reload is single threaded.developmentenvironment can load code lazily once the request is fired which results in first request to always be slow.
To disable those features for profiling/benchmarking set the RAILS_PROFILE environment variable to true before starting GitLab. For example when using GDK:
- create a file
env.runitin the root GDK directory - add
export RAILS_PROFILE=trueto yourenv.runitfile - restart GDK with
gdk restart
This environment variable is only applicable for the development mode.
GC settings
Ruby's garbage collector (GC) can be tuned via a variety of environment variables that will directly impact application performance.
The following table lists these variables along with their default values.
| Environment variable | Default value |
|---|---|
RUBY_GC_HEAP_INIT_SLOTS |
10000 |
RUBY_GC_HEAP_FREE_SLOTS |
4096 |
RUBY_GC_HEAP_FREE_SLOTS_MIN_RATIO |
0.20 |
RUBY_GC_HEAP_FREE_SLOTS_GOAL_RATIO |
0.40 |
RUBY_GC_HEAP_FREE_SLOTS_MAX_RATIO |
0.65 |
RUBY_GC_HEAP_GROWTH_FACTOR |
1.8 |
RUBY_GC_HEAP_GROWTH_MAX_SLOTS |
0 (disable) |
RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR |
2.0 |
RUBY_GC_MALLOC_LIMIT(_MIN) |
(16 * 1024 * 1024 /* 16MB */) |
RUBY_GC_MALLOC_LIMIT_MAX |
(32 * 1024 * 1024 /* 32MB */) |
RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR |
1.4 |
RUBY_GC_OLDMALLOC_LIMIT(_MIN) |
(16 * 1024 * 1024 /* 16MB */) |
RUBY_GC_OLDMALLOC_LIMIT_MAX |
(128 * 1024 * 1024 /* 128MB */) |
RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR |
1.2 |
(Source)
GitLab may decide to change these settings to speed up application performance, lower memory requirements, or both.
You can see how each of these settings affect GC performance, memory use and application start-up time for an idle instance of
GitLab by running the scripts/perf/gc/collect_gc_stats.rb script. It will output GC stats and general timing data to standard
out as CSV.