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stage | group | info | type |
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Create | Gitaly | To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments | reference |
Gitaly developers guide
Gitaly is a high-level Git RPC service used by GitLab Rails, Workhorse and GitLab Shell.
Deep Dive
In May 2019, Bob Van Landuyt
hosted a Deep Dive (GitLab team members only: https://gitlab.com/gitlab-org/create-stage/issues/1
)
on the Gitaly project. It included how to contribute to it as a
Ruby developer, and shared domain-specific knowledge with anyone who may work in this part of the
codebase in the future.
You can find the recording on YouTube, and the slides on Google Slides and in PDF.
Everything covered in this deep dive was accurate as of GitLab 11.11, and while specific details may have changed, it should still serve as a good introduction.
Beginner's guide
Start by reading the Gitaly repository's Beginner's guide to Gitaly contributions. It describes how to set up Gitaly, the various components of Gitaly and what they do, and how to run its test suites.
Developing new Git features
To read or write Git data, a request has to be made to Gitaly. This means that
if you're developing a new feature where you need data that's not yet available
in lib/gitlab/git
changes have to be made to Gitaly.
There should be no new code that touches Git repositories via disk access (for example,
Rugged, git
, rm -rf
) anywhere in the gitlab
repository. Anything that
needs direct access to the Git repository must be implemented in Gitaly, and
exposed via an RPC.
It's often easier to develop a new feature in Gitaly if you make the changes to GitLab that intends to use the new feature in a separate merge request, to be merged immediately after the Gitaly one. This allows you to test your changes before they are merged.
- See below for instructions on running GitLab tests with a modified version of Gitaly.
- In GDK run
gdk install
and restart GDK usinggdk restart
to use a locally modified Gitaly version for development
gitaly-ruby
It is possible to implement and test RPC's in Gitaly using Ruby code,
in
gitaly-ruby
.
This should make it easier to contribute for developers who are less
comfortable writing Go code.
For more information, see the Beginner's guide to Gitaly contributions.
Gitaly-Related Test Failures
If your test-suite is failing with Gitaly issues, as a first step, try running:
rm -rf tmp/tests/gitaly
During RSpec tests, the Gitaly instance writes logs to gitlab/log/gitaly-test.log
.
Legacy Rugged code
While Gitaly can handle all Git access, many of GitLab customers still run Gitaly atop NFS. The legacy Rugged implementation for Git calls may be faster than the Gitaly RPC due to N+1 Gitaly calls and other reasons. See the issue for more details.
Until GitLab has eliminated most of these inefficiencies or the use of NFS is discontinued for Git data, Rugged implementations of some of the most commonly-used RPCs can be enabled via feature flags:
rugged_find_commit
rugged_get_tree_entries
rugged_tree_entry
rugged_commit_is_ancestor
rugged_commit_tree_entry
rugged_list_commits_by_oid
A convenience Rake task can be used to enable or disable these flags all together. To enable:
bundle exec rake gitlab:features:enable_rugged
To disable:
bundle exec rake gitlab:features:disable_rugged
Most of this code exists in the lib/gitlab/git/rugged_impl
directory.
NOTE: You should not have to add or modify code related to Rugged unless explicitly discussed with the Gitaly Team. This code does not work on GitLab.com or other GitLab instances that do not use NFS.
TooManyInvocationsError
errors
During development and testing, you may experience Gitlab::GitalyClient::TooManyInvocationsError
failures.
The GitalyClient
attempts to block against potential n+1 issues by raising this error
when Gitaly is called more than 30 times in a single Rails request or Sidekiq execution.
As a temporary measure, export GITALY_DISABLE_REQUEST_LIMITS=1
to suppress the error. This disables the n+1 detection
in your development environment.
Please raise an issue in the GitLab CE or EE repositories to report the issue. Include the labels ~Gitaly
~performance ~"technical debt". Please ensure that the issue contains the full stack trace and error message of the
TooManyInvocationsError
. Also include any known failing tests if possible.
Isolate the source of the n+1 problem. This is normally a loop that results in Gitaly being called for each element in an array. If you are unable to isolate the problem, please contact a member of the Gitaly Team for assistance.
After the source has been found, wrap it in an allow_n_plus_1_calls
block, as follows:
# n+1: link to n+1 issue
Gitlab::GitalyClient.allow_n_plus_1_calls do
# original code
commits.each { |commit| ... }
end
After the code is wrapped in this block, this code path is excluded from n+1 detection.
Request counts
Commits and other Git data, is now fetched through Gitaly. These fetches can,
much like with a database, be batched. This improves performance for the client
and for Gitaly itself and therefore for the users too. To keep performance stable
and guard performance regressions, Gitaly calls can be counted and the call count
can be tested against. This requires the :request_store
flag to be set.
describe 'Gitaly Request count tests' do
context 'when the request store is activated', :request_store do
it 'correctly counts the gitaly requests made' do
expect { subject }.to change { Gitlab::GitalyClient.get_request_count }.by(10)
end
end
end
Running tests with a locally modified version of Gitaly
Normally, GitLab CE/EE tests use a local clone of Gitaly in
tmp/tests/gitaly
pinned at the version specified in
GITALY_SERVER_VERSION
. The GITALY_SERVER_VERSION
file supports also
branches and SHA to use a custom commit in the repository.
NOTE:
With the introduction of auto-deploy for Gitaly, the format of
GITALY_SERVER_VERSION
was aligned with Omnibus syntax.
It no longer supports =revision
, it evaluates the file content as a Git
reference (branch or SHA). Only if it matches a semantic version does it prepend a v
.
If you want to run tests locally against a modified version of Gitaly you
can replace tmp/tests/gitaly
with a symlink. This is much faster
because it avoids a Gitaly re-install each time you run rspec
.
Make sure this directory contains the files config.toml
and praefect.config.toml
.
You can copy them from config.toml.example
and config.praefect.toml.example
respectively.
After copying, make sure to edit them so everything points to the correct paths.
rm -rf tmp/tests/gitaly
ln -s /path/to/gitaly tmp/tests/gitaly
Make sure you run make
in your local Gitaly directory before running
tests. Otherwise, Gitaly fails to boot.
If you make changes to your local Gitaly in between test runs you need
to manually run make
again.
Note that CI tests do not use your locally modified version of Gitaly. To use a custom Gitaly version in CI, you must update GITALY_SERVER_VERSION as described at the beginning of this section.
To use a different Gitaly repository, such as if your changes are present
on a fork, you can specify a GITALY_REPO_URL
environment variable when
running tests:
GITALY_REPO_URL=https://gitlab.com/nick.thomas/gitaly bundle exec rspec spec/lib/gitlab/git/repository_spec.rb
If your fork of Gitaly is private, you can generate a Deploy Token and specify it in the URL:
GITALY_REPO_URL=https://gitlab+deploy-token-1000:token-here@gitlab.com/nick.thomas/gitaly bundle exec rspec spec/lib/gitlab/git/repository_spec.rb
To use a custom Gitaly repository in CI/CD, for instance if you want your
GitLab fork to always use your own Gitaly fork, set GITALY_REPO_URL
as a CI/CD variable.
Use a locally modified version of Gitaly RPC client
If you are making changes to the RPC client, such as adding a new endpoint or adding a new
parameter to an existing endpoint, follow the guide for
Gitaly protobuf specifications. After pushing
the branch with the changes (new-feature-branch
, for example):
-
Change the
gitaly
line in the Rails'Gemfile
to:gem 'gitaly', git: 'https://gitlab.com/gitlab-org/gitaly.git', branch: 'new-feature-branch'
-
Run
bundle install
to use the modified RPC client.
Re-run bundle install
in the gitlab
project each time the Gitaly branch
changes to embed a new SHA in the Gemfile.lock
file.
Return to Development documentation
Wrapping RPCs in Feature Flags
Here are the steps to gate a new feature in Gitaly behind a feature flag.
Gitaly
-
Create a package scoped flag name:
var findAllTagsFeatureFlag = "go-find-all-tags"
-
Create a switch in the code using the
featureflag
package:if featureflag.IsEnabled(ctx, findAllTagsFeatureFlag) { // go implementation } else { // ruby implementation }
-
Create Prometheus metrics:
var findAllTagsRequests = prometheus.NewCounterVec( prometheus.CounterOpts{ Name: "gitaly_find_all_tags_requests_total", Help: "Counter of go vs ruby implementation of FindAllTags", }, []string{"implementation"}, ) func init() { prometheus.Register(findAllTagsRequests) } if featureflag.IsEnabled(ctx, findAllTagsFeatureFlag) { findAllTagsRequests.WithLabelValues("go").Inc() // go implementation } else { findAllTagsRequests.WithLabelValues("ruby").Inc() // ruby implementation }
-
Set headers in tests:
import ( "google.golang.org/grpc/metadata" "gitlab.com/gitlab-org/gitaly/internal/featureflag" ) //... md := metadata.New(map[string]string{featureflag.HeaderKey(findAllTagsFeatureFlag): "true"}) ctx = metadata.NewOutgoingContext(context.Background(), md) c, err = client.FindAllTags(ctx, rpcRequest) require.NoError(t, err)
GitLab Rails
Test in a Rails console by setting the feature flag:
Feature.enable('gitaly_go_find_all_tags')
Pay attention to the name of the flag and the one used in the Rails console. There is a difference
between them (dashes replaced by underscores and name prefix is changed). Make sure to prefix all
flags with gitaly_
.
NOTE: If not set in GitLab, feature flags are read as false from the console and Gitaly uses their default value. The default value depends on the GitLab version.
Testing with GDK
To be sure that the flag is set correctly and it goes into Gitaly, you can check the integration by using GDK:
-
The state of the flag must be observable. To check it, you must enable it by fetching the Prometheus metrics:
- Navigate to GDK's root directory.
- Make sure you have the proper branch checked out for Gitaly.
- Recompile it with
make gitaly-setup
and restart the service withgdk restart gitaly
. - Make sure your setup is running:
gdk status | grep praefect
. - Check what configuration file is used:
cat ./services/praefect/run | grep praefect
value of the-config
flag - Uncomment
prometheus_listen_addr
in the configuration file and rungdk restart gitaly
.
-
Make sure that the flag is not enabled yet:
-
Perform whatever action is required to trigger your changes, such as project creation, submitting commit, or observing history.
-
Check that the list of current metrics has the new counter for the feature flag:
curl --silent "http://localhost:9236/metrics" | grep go_find_all_tags
-
-
After you observe the metrics for the new feature flag and it increments, you can enable the new feature:
-
Navigate to GDK's root directory.
-
Start a Rails console:
bundle install && bundle exec rails console
-
Check the list of feature flags:
Feature::Gitaly.server_feature_flags
It should be disabled
"gitaly-feature-go-find-all-tags"=>"false"
. -
Enable it:
Feature.enable('gitaly_go_find_all_tags')
-
Exit the Rails console and perform whatever action is required to trigger your changes, such as project creation, submitting commit, or observing history.
-
Verify the feature is on by observing the metrics for it:
curl --silent "http://localhost:9236/metrics" | grep go_find_all_tags
-