d13669716a
In GitLab EE, a GitLab instance can be read-only (e.g. when it's a Geo secondary node). But in GitLab CE it also might be useful to have the "read-only" idea around. So port it back to GitLab CE. Also having the principle of read-only in GitLab CE would hopefully lead to less errors introduced, doing write operations when there aren't allowed for read-only calls. Closes gitlab-org/gitlab-ce#37534.
38 lines
1.4 KiB
Markdown
38 lines
1.4 KiB
Markdown
# Verifying Database Capabilities
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Sometimes certain bits of code may only work on a certain database and/or
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version. While we try to avoid such code as much as possible sometimes it is
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necessary to add database (version) specific behaviour.
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To facilitate this we have the following methods that you can use:
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* `Gitlab::Database.postgresql?`: returns `true` if PostgreSQL is being used
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* `Gitlab::Database.mysql?`: returns `true` if MySQL is being used
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* `Gitlab::Database.version`: returns the PostgreSQL version number as a string
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in the format `X.Y.Z`. This method does not work for MySQL
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This allows you to write code such as:
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```ruby
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if Gitlab::Database.postgresql?
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if Gitlab::Database.version.to_f >= 9.6
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run_really_fast_query
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else
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run_fast_query
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end
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else
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run_query
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end
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```
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# Read-only database
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The database can be used in read-only mode. In this case we have to
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make sure all GET requests don't attempt any write operations to the
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database. If one of those requests wants to write to the database, it needs
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to be wrapped in a `Gitlab::Database.read_only?` or `Gitlab::Database.read_write?`
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guard, to make sure it doesn't for read-only databases.
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We have a Rails Middleware that filters any potentially writing
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operations (the CUD operations of CRUD) and prevent the user from trying
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to update the database and getting a 500 error (see `Gitlab::Middleware::ReadOnly`).
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