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

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---
comments: false
description: 'Learn how to contribute to GitLab.'
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---
# GitLab development guides
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## 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
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- [Frontend guidelines](fe_guide/index.md)
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- [Emoji guide](fe_guide/emojis.md)
## Backend guides
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- [GitLab utilities](utilities.md)
- [Logging](logging.md)
- [API styleguide](api_styleguide.md) Use this styleguide if you are
contributing to the API.
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- [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)
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- [Pry debugging](pry_debugging.md)
- [Sidekiq debugging](sidekiq_debugging.md)
- [Gotchas](gotchas.md) to avoid
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- [Avoid modules with instance variables](module_with_instance_variables.md) if possible
- [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.
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- [Working with the GitHub importer](github_importer.md)
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- [Import/Export development documentation](import_export.md)
- [Working with Merge Request diffs](diffs.md)
- [Permissions](permissions.md)
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- [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)
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- [Markdown](../user/markdown.md)
## Internationalization (i18n) guides
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- [Introduction](i18n/index.md)
- [Externalization](i18n/externalization.md)
- [Translation](i18n/translation.md)
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## Build guides
- [Building a package for testing purposes](build_test_package.md)
## Compliance
- [Licensing](licensing.md) for ensuring license compliance