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Merge branch 'fix-doc-on-migration' into 'master'

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Fix doc for large table column rename

See merge request gitlab-org/gitlab-ce!20544
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Sean McGivern 2018-07-11 08:32:32 +00:00
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doc/development/what_requires_downtime.md
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@ -198,14 +198,14 @@ And that's it, we're done!
## Changing The Schema For Large Tables
While `change_column_type_concurrently` and `rename_column_concurrently` can be
used for changing the schema of a table without downtime it doesn't work very
used for changing the schema of a table without downtime, it doesn't work very
well for large tables. Because all of the work happens in sequence the migration
can take a very long time to complete, preventing a deployment from proceeding.
They can also produce a lot of pressure on the database due to it rapidly
updating many rows in sequence.
To reduce database pressure you should instead use
`change_column_type_using_background_migration` or `rename_column_concurrently`
`change_column_type_using_background_migration` or `rename_column_using_background_migration`
when migrating a column in a large table (e.g. `issues`). These methods work
similarly to the concurrent counterparts but uses background migration to spread
the work / load over a longer time period, without slowing down deployments.