38 lines
1.4 KiB
Markdown
38 lines
1.4 KiB
Markdown
---
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stage: Data Stores
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group: Database
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info: 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
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---
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# Verifying Database Capabilities
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Sometimes certain bits of code may only work on a certain database
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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 behavior.
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To facilitate this we have the following methods that you can use:
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- `ApplicationRecord.database.version`: returns the PostgreSQL version number as a string
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in the format `X.Y.Z`.
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This allows you to write code such as:
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```ruby
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if ApplicationRecord.database.version.to_f >= 11.7
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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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```
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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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