49 lines
2.2 KiB
Markdown
49 lines
2.2 KiB
Markdown
---
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stage: none
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group: unassigned
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info: Any user with at least the Maintainer role can merge updates to this content. For details, see https://docs.gitlab.com/ee/development/development_processes.html#development-guidelines-review.
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---
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# Rails initializers
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Initializers are executed when the Rails process is started. That means that initializers are also executed during every deploy.
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By default, Rails loads Zeitwerk after the initializers in `config/initializers` are loaded.
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Autoloading before Zeitwerk is loaded is now deprecated but because we use a lot of autoloaded
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constants in our initializers, we had to move the loading of Zeitwerk earlier than these
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initializers.
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A side-effect of this is that in the initializers, `config.autoload_paths` is already frozen.
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To run an initializer before Zeitwerk is loaded, you need put them in `config/initializers_before_autoloader`.
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Ruby files in this folder are loaded in alphabetical order just like the default Rails initializers.
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Some examples where you would need to do this are:
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1. Modifying Rails' `config.autoload_paths`
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1. Changing configuration that Zeitwerk uses, for example, inflections
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## Database connections in initializers
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Ideally, database connections are not opened from Rails initializers. Opening a
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database connection (for example, checking the database exists, or making a database
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query) from an initializer means that tasks like `db:drop`, and
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`db:test:prepare` will fail because an active session prevents the database from
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being dropped.
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To prevent this, we stop database connections from being opened during
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routes loading. Doing will result in an error:
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```shell
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RuntimeError:
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Database connection should not be called during initializers.
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# ./config/initializers/00_connection_logger.rb:15:in `new_client'
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# ./lib/gitlab/database/load_balancing/load_balancer.rb:112:in `block in read_write'
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# ./lib/gitlab/database/load_balancing/load_balancer.rb:184:in `retry_with_backoff'
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# ./lib/gitlab/database/load_balancing/load_balancer.rb:111:in `read_write'
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# ./lib/gitlab/database/load_balancing/connection_proxy.rb:119:in `write_using_load_balancer'
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# ./lib/gitlab/database/load_balancing/connection_proxy.rb:89:in `method_missing'
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# ./config/routes.rb:10:in `block in <main>'
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# ./config/routes.rb:9:in `<main>'
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```
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