gitlab-org--gitlab-foss/doc/development/README.md

---
comments: false
description: 'Learn how to contribute to GitLab.'
---

# GitLab development guides

## Get started!

- Set up GitLab's development environment with [GitLab Development Kit (GDK)](https://gitlab.com/gitlab-org/gitlab-development-kit/blob/master/doc/howto/README.md)
- [GitLab contributing guide](contributing/index.md)
- [Architecture](architecture.md) of GitLab
- [Rake tasks](rake_tasks.md) for development

## Processes

- [GitLab core team & GitLab Inc. contribution process](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/PROCESS.md)
- [Generate a changelog entry with `bin/changelog`](changelog.md)
- [Code review guidelines](code_review.md) for reviewing code and having code reviewed.
- [Automatic CE->EE merge](automatic_ce_ee_merge.md)
- [Guidelines for implementing Enterprise Edition features](ee_features.md)
- [Security process for developers](https://gitlab.com/gitlab-org/release/docs/blob/master/general/security/developer.md#security-releases-critical-non-critical-as-a-developer)

## UX and frontend guides

- [GitLab Design System](https://design.gitlab.com/) for building GitLab with existing CSS styles and elements
- [Frontend guidelines](fe_guide/index.md)
- [Emoji guide](fe_guide/emojis.md)

## Backend guides

- [GitLab utilities](utilities.md)
- [Logging](logging.md)
- [API styleguide](api_styleguide.md) Use this styleguide if you are
  contributing to the API.
- [GraphQL API styleguide](api_graphql_styleguide.md) Use this
  styleguide if you are contribution to the [GraphQL API](../api/graphql/index.md)
- [Sidekiq guidelines](sidekiq_style_guide.md) for working with Sidekiq workers
- [Working with Gitaly](gitaly.md)
- [Manage feature flags](feature_flags.md)
- [View sent emails or preview mailers](emails.md)
- [Shell commands](shell_commands.md) in the GitLab codebase
- [`Gemfile` guidelines](gemfile.md)
- [Pry debugging](pry_debugging.md)
- [Sidekiq debugging](sidekiq_debugging.md)
- [Gotchas](gotchas.md) to avoid
- [Avoid modules with instance variables](module_with_instance_variables.md) if possible
- [How to dump production data to staging](db_dump.md)
- [Working with the GitHub importer](github_importer.md)
- [Working with Merge Request diffs](diffs.md)
- [Permissions](permissions.md)
- [Prometheus metrics](prometheus_metrics.md)
- [Guidelines for reusing abstractions](reusing_abstractions.md)
- [DeclarativePolicy framework](policies.md)

## Performance guides

- [Instrumentation](instrumentation.md) for Ruby code running in production
  environments
- [Performance guidelines](performance.md) for writing code, benchmarks, and
  certain patterns to avoid
- [Merge request performance guidelines](merge_request_performance_guidelines.md)
  for ensuring merge requests do not negatively impact GitLab performance
- [Profiling](profiling.md) a URL, measuring performance using Sherlock, or
  tracking down N+1 queries using Bullet

## Database guides

### Tooling

- [Understanding EXPLAIN plans](understanding_explain_plans.md)
- [explain.depesz.com](https://explain.depesz.com/) for visualising the output
  of `EXPLAIN`

### Migrations

- [What requires downtime?](what_requires_downtime.md)
- [SQL guidelines](sql.md) for working with SQL queries
- [Migrations style guide](migration_style_guide.md) for creating safe SQL migrations
- [Post deployment migrations](post_deployment_migrations.md)
- [Background migrations](background_migrations.md)
- [Swapping tables](swapping_tables.md)

### Best practices

- [Merge Request checklist](database_merge_request_checklist.md)
- [Adding database indexes](adding_database_indexes.md)
- [Foreign keys & associations](foreign_keys.md)
- [Single table inheritance](single_table_inheritance.md)
- [Polymorphic associations](polymorphic_associations.md)
- [Serializing data](serializing_data.md)
- [Hash indexes](hash_indexes.md)
- [Storing SHA1 hashes as binary](sha1_as_binary.md)
- [Iterating tables in batches](iterating_tables_in_batches.md)
- [Ordering table columns](ordering_table_columns.md)
- [Verifying database capabilities](verifying_database_capabilities.md)
- [Database Debugging and Troubleshooting](database_debugging.md)
- [Query Count Limits](query_count_limits.md)
- [Database helper modules](database_helpers.md)

## Testing guides

- [Testing standards and style guidelines](testing_guide/index.md)
- [Frontend testing standards and style guidelines](testing_guide/frontend_testing.md)

## Documentation guides

- [Writing documentation](documentation/index.md)
- [Documentation styleguide](documentation/styleguide.md)
- [Markdown](../user/markdown.md)

## Internationalization (i18n) guides

- [Introduction](i18n/index.md)
- [Externalization](i18n/externalization.md)
- [Translation](i18n/translation.md)

## Build guides

- [Building a package for testing purposes](build_test_package.md)

## Compliance

- [Licensing](licensing.md) for ensuring license compliance
Exclude comments from specific docs 2017-11-01 11:56:40 -04:00			`---`
			`comments: false`
Docs: add custom descriptions to most relevant docs 2018-05-09 07:07:11 -04:00			`description: 'Learn how to contribute to GitLab.'`
Exclude comments from specific docs 2017-11-01 11:56:40 -04:00			`---`

Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`# GitLab development guides`
Add doc file for dev rake tasks 2014-04-24 13:53:18 -04:00
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`## Get started!`
Structure the development documentation 2016-08-04 06:45:59 -04:00
Correct grammar (setup to set-up) in Docs 2018-09-19 12:03:00 -04:00			`- Set up GitLab's development environment with [GitLab Development Kit (GDK)](https://gitlab.com/gitlab-org/gitlab-development-kit/blob/master/doc/howto/README.md)`
Improve the contributing documentation This removes duplicated content from CONTRIBUTING.md and consolidate everything under doc/development/contributing/. This also fixes missing links. Lastly, this moves the style guides from the "Implement design & UI elements" page to a new "Style guides" page. Signed-off-by: Rémy Coutable <remy@rymai.me> 2018-10-11 07:57:49 -04:00			`- [GitLab contributing guide](contributing/index.md)`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`- [Architecture](architecture.md) of GitLab`
			`- [Rake tasks](rake_tasks.md) for development`
Structure the development documentation 2016-08-04 06:45:59 -04:00
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`## Processes`

			`- [GitLab core team & GitLab Inc. contribution process](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/PROCESS.md)`
			- [Generate a changelog entry with `bin/changelog`](changelog.md)
			`- [Code review guidelines](code_review.md) for reviewing code and having code reviewed.`
Move the "Limit conflicts with EE" doc to "Automatic CE-> EE merge" Signed-off-by: Rémy Coutable <remy@rymai.me> 2017-12-05 11:49:49 -05:00			`- [Automatic CE->EE merge](automatic_ce_ee_merge.md)`
Add "Guidelines for implementing Enterprise Edition features" in CE development doc since the doc page is already there Signed-off-by: Rémy Coutable <remy@rymai.me> 2017-12-06 11:23:53 -05:00			`- [Guidelines for implementing Enterprise Edition features](ee_features.md)`
Add missing security process for developers 2018-05-08 06:55:02 -04:00			`- [Security process for developers](https://gitlab.com/gitlab-org/release/docs/blob/master/general/security/developer.md#security-releases-critical-non-critical-as-a-developer)`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00
			`## UX and frontend guides`
Structure the development documentation 2016-08-04 06:45:59 -04:00
deprecate UX Guide and redirect to design.gitlab 2018-11-21 10:25:15 -05:00			`- [GitLab Design System](https://design.gitlab.com/) for building GitLab with existing CSS styles and elements`
Creates Frontend Style guide 2017-03-22 15:30:54 -04:00			`- [Frontend guidelines](fe_guide/index.md)`
Add basic emoji development docs 2017-11-14 17:29:33 -05:00			`- [Emoji guide](fe_guide/emojis.md)`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00
			`## Backend guides`

Add documents for GitLab utilities 2017-12-29 01:29:53 -05:00			`- [GitLab utilities](utilities.md)`
Add documentation on how to use structured logging 2018-11-13 17:43:16 -05:00			`- [Logging](logging.md)`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`- [API styleguide](api_styleguide.md) Use this styleguide if you are`
			`contributing to the API.`
Fix typo in doc/development/README.md 2018-06-11 23:28:29 -04:00			`- [GraphQL API styleguide](api_graphql_styleguide.md) Use this`
Add `present_using` to types By specifying a presenter for the object type, we can keep the logic out of `GitlabSchema`. The presenter gets initialized using the object being presented, and the context (including the `current_user`). 2018-05-21 03:52:24 -04:00			`styleguide if you are contribution to the [GraphQL API](../api/graphql/index.md)`
Re-organize queues to use for Sidekiq Dumping too many jobs in the same queue (e.g. the "default" queue) is a dangerous setup. Jobs that take a long time to process can effectively block any other work from being performed given there are enough of these jobs. Furthermore it becomes harder to monitor the jobs as a single queue could contain jobs for different workers. In such a setup the only reliable way of getting counts per job is to iterate over all jobs in a queue, which is a rather time consuming process. By using separate queues for various workers we have better control over throughput, we can add weight to queues, and we can monitor queues better. Some workers still use the same queue whenever their work is related. For example, the various CI pipeline workers use the same "pipeline" queue. This commit includes a Rails migration that moves Sidekiq jobs from the old queues to the new ones. This migration also takes care of doing the inverse if ever needed. This does require downtime as otherwise new jobs could be scheduled in the old queues after this migration completes. This commit also includes an RSpec test that blacklists the use of the "default" queue and ensures cron workers use the "cronjob" queue. Fixes gitlab-org/gitlab-ce#23370 2016-10-21 12:13:41 -04:00			`- [Sidekiq guidelines](sidekiq_style_guide.md) for working with Sidekiq workers`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`- [Working with Gitaly](gitaly.md)`
			`- [Manage feature flags](feature_flags.md)`
			`- [View sent emails or preview mailers](emails.md)`
			`- [Shell commands](shell_commands.md) in the GitLab codebase`
Document "No gems fetched from git repositories" policy [ci skip] 2017-01-27 06:17:21 -05:00			- [`Gemfile` guidelines](gemfile.md)
First version of pry_debugging.md 2018-07-20 01:31:51 -04:00			`- [Pry debugging](pry_debugging.md)`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`- [Sidekiq debugging](sidekiq_debugging.md)`
			`- [Gotchas](gotchas.md) to avoid`
Updates based on feedback 2017-11-21 10:15:24 -05:00			`- [Avoid modules with instance variables](module_with_instance_variables.md) if possible`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`- [How to dump production data to staging](db_dump.md)`
Rewrite the GitHub importer from scratch Prior to this MR there were two GitHub related importers: * Github::Import: the main importer used for GitHub projects * Gitlab::GithubImport: importer that's somewhat confusingly used for importing Gitea projects (apparently they have a compatible API) This MR renames the Gitea importer to Gitlab::LegacyGithubImport and introduces a new GitHub importer in the Gitlab::GithubImport namespace. This new GitHub importer uses Sidekiq for importing multiple resources in parallel, though it also has the ability to import data sequentially should this be necessary. The new code is spread across the following directories: * lib/gitlab/github_import: this directory contains most of the importer code such as the classes used for importing resources. * app/workers/gitlab/github_import: this directory contains the Sidekiq workers, most of which simply use the code from the directory above. * app/workers/concerns/gitlab/github_import: this directory provides a few modules that are included in every GitHub importer worker. == Stages The import work is divided into separate stages, with each stage importing a specific set of data. Stages will schedule the work that needs to be performed, followed by scheduling a job for the "AdvanceStageWorker" worker. This worker will periodically check if all work is completed and schedule the next stage if this is the case. If work is not yet completed this worker will reschedule itself. Using this approach we don't have to block threads by calling `sleep()`, as doing so for large projects could block the thread from doing any work for many hours. == Retrying Work Workers will reschedule themselves whenever necessary. For example, hitting the GitHub API's rate limit will result in jobs rescheduling themselves. These jobs are not processed until the rate limit has been reset. == User Lookups Part of the importing process involves looking up user details in the GitHub API so we can map them to GitLab users. The old importer used an in-memory cache, but this obviously doesn't work when the work is spread across different threads. The new importer uses a Redis cache and makes sure we only perform API/database calls if absolutely necessary. Frequently used keys are refreshed, and lookup misses are also cached; removing the need for performing API/database calls if we know we don't have the data we're looking for. == Performance & Models The new importer in various places uses raw INSERT statements (as generated by `Gitlab::Database.bulk_insert`) instead of using Rails models. This allows us to bypass any validations and callbacks, drastically reducing the number of SQL queries and Gitaly RPC calls necessary to import projects. To ensure the code produces valid data the corresponding tests check if the produced rows are valid according to the model validation rules. 2017-10-13 12:50:36 -04:00			`- [Working with the GitHub importer](github_importer.md)`
Add developer documentation on diff handling and limits 2018-04-09 17:24:26 -04:00			`- [Working with Merge Request diffs](diffs.md)`
Document permissions for different entities 2018-09-10 06:54:52 -04:00			`- [Permissions](permissions.md)`
Add development documentation 2018-09-04 09:01:34 -04:00			`- [Prometheus metrics](prometheus_metrics.md)`
Document abstraction levels and code reuse This is based on the discussion in https://gitlab.com/gitlab-org/gitlab-ce/issues/49653 and the example merge request found at https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20908. The idea is fairly straightforward: we define a variety of abstractions, then state which can reuse which. This should ultimately foster _better_ code reuse, make it easier to debug problems, and make it harder to accidentally introduce a performance regression. 2018-08-16 11:14:14 -04:00			`- [Guidelines for reusing abstractions](reusing_abstractions.md)`
Link to DeclarativePolicy page from /development 2018-10-14 18:58:29 -04:00			`- [DeclarativePolicy framework](policies.md)`
Structure the development documentation 2016-08-04 06:45:59 -04:00
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`## Performance guides`
Structure the development documentation 2016-08-04 06:45:59 -04:00
Enhance some performance guideline titles This enhances a few performance guideline titles in the development README, making it easier to understand what topics they cover. 2018-09-18 08:25:22 -04:00			`- [Instrumentation](instrumentation.md) for Ruby code running in production`
			`environments`
			`- [Performance guidelines](performance.md) for writing code, benchmarks, and`
			`certain patterns to avoid`
Added performance guidelines for new MRs These guidelines cover the performance requirement for newly submitted merge requests. These guidelines are put in to place to prevent merge requests from negatively impacting GitLab performance as much as possible. 2016-08-19 11:21:00 -04:00			`- [Merge request performance guidelines](merge_request_performance_guidelines.md)`
			`for ensuring merge requests do not negatively impact GitLab performance`
Remove redundant word from development doc index 2018-09-18 16:17:07 -04:00			`- [Profiling](profiling.md) a URL, measuring performance using Sherlock, or`
			`tracking down N+1 queries using Bullet`
Structure the development documentation 2016-08-04 06:45:59 -04:00
Add documentation about reading query plans This adds a database guide on how to read the output of "EXPLAIN" and "EXPLAIN ANALYZE", and how to use this output to understand a query's performance and optimise it. 2018-08-14 12:07:15 -04:00			`## Database guides`

			`### Tooling`

			`- [Understanding EXPLAIN plans](understanding_explain_plans.md)`
			`- [explain.depesz.com](https://explain.depesz.com/) for visualising the output`
			of `EXPLAIN`
Added documentation on adding database indexes 2016-08-11 08:22:21 -04:00
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`### Migrations`
Added documentation on adding database indexes 2016-08-11 08:22:21 -04:00
Added guide about migrations and downtime This guide describes various commonly used operations and the impact they have on the availability of a GitLab instance. 2016-08-04 11:17:31 -04:00			`- [What requires downtime?](what_requires_downtime.md)`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`- [SQL guidelines](sql.md) for working with SQL queries`
			`- [Migrations style guide](migration_style_guide.md) for creating safe SQL migrations`
			`- [Post deployment migrations](post_deployment_migrations.md)`
			`- [Background migrations](background_migrations.md)`
			`- [Swapping tables](swapping_tables.md)`

			`### Best practices`

			`- [Merge Request checklist](database_merge_request_checklist.md)`
Added documentation on adding database indexes 2016-08-11 08:22:21 -04:00			`- [Adding database indexes](adding_database_indexes.md)`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`- [Foreign keys & associations](foreign_keys.md)`
			`- [Single table inheritance](single_table_inheritance.md)`
			`- [Polymorphic associations](polymorphic_associations.md)`
			`- [Serializing data](serializing_data.md)`
			`- [Hash indexes](hash_indexes.md)`
			`- [Storing SHA1 hashes as binary](sha1_as_binary.md)`
			`- [Iterating tables in batches](iterating_tables_in_batches.md)`
			`- [Ordering table columns](ordering_table_columns.md)`
			`- [Verifying database capabilities](verifying_database_capabilities.md)`
Add basic docs for troubleshooting database problems 2017-11-15 22:19:14 -05:00			`- [Database Debugging and Troubleshooting](database_debugging.md)`
Track and act upon the number of executed queries This ensures that we have more visibility in the number of SQL queries that are executed in web requests. The current threshold is hardcoded to 100 as we will rarely (maybe once or twice) change it. In production and development we use Sentry if enabled, in the test environment we raise an error. This feature is also only enabled in production/staging when running on GitLab.com as it's not very useful to other users. 2018-01-15 10:21:04 -05:00			`- [Query Count Limits](query_count_limits.md)`
Add Gitlab::Database::Subquery.self_join to delete_all with limit `delete_all` doesn't support limit, so you'd need to subquery that. And instead of subquerying with `where(id: query)`, it's better to use an `INNER JOIN`. This method also works with MySQL, while subquerying doesn't (without another layer of subquerying) Reference: https://stackoverflow.com/questions/17892762/mysql-this-version-of-mysql-doesnt-yet-support-limit-in-all-any-some-subqu/17892886#17892886 2018-09-18 11:32:21 -04:00			`- [Database helper modules](database_helpers.md)`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00
Fix a missing link and create a separate "Testing guides" section Signed-off-by: Rémy Coutable <remy@rymai.me> 2017-10-11 10:33:57 -04:00			`## Testing guides`

			`- [Testing standards and style guidelines](testing_guide/index.md)`
			`- [Frontend testing standards and style guidelines](testing_guide/frontend_testing.md)`

Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`## Documentation guides`

Docs: add the documentation guidelines into its own dir 2018-06-06 07:32:38 -04:00			`- [Writing documentation](documentation/index.md)`
			`- [Documentation styleguide](documentation/styleguide.md)`
Docs update documentation guidelines 2017-12-15 05:56:21 -05:00			`- [Markdown](../user/markdown.md)`
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00
			`## Internationalization (i18n) guides`
Add guide to collaborate with i18n. 2017-05-16 14:26:12 -04:00
Move i18n/introduction to i18n/index 2017-10-09 05:28:01 -04:00			`- [Introduction](i18n/index.md)`
Docs: add translation and proof reading guidelines 2017-09-26 17:15:19 -04:00			`- [Externalization](i18n/externalization.md)`
			`- [Translation](i18n/translation.md)`
Add guide to collaborate with i18n. 2017-05-16 14:26:12 -04:00
Refactor the Development documentation, and divide the Testing documentation into multiple pages 2017-10-11 01:59:34 -04:00			`## Build guides`

			`- [Building a package for testing purposes](build_test_package.md)`

Structure the development documentation 2016-08-04 06:45:59 -04:00			`## Compliance`

			`- [Licensing](licensing.md) for ensuring license compliance`