Commit 078c824f authored by Sean McGivern's avatar Sean McGivern

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

Fix doc for large table column rename

See merge request gitlab-org/gitlab-ce!20544
parents c6b67021 2be54f1b
...@@ -198,14 +198,14 @@ And that's it, we're done! ...@@ -198,14 +198,14 @@ And that's it, we're done!
## Changing The Schema For Large Tables ## Changing The Schema For Large Tables
While `change_column_type_concurrently` and `rename_column_concurrently` can be 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 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. 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 They can also produce a lot of pressure on the database due to it rapidly
updating many rows in sequence. updating many rows in sequence.
To reduce database pressure you should instead use 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 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 similarly to the concurrent counterparts but uses background migration to spread
the work / load over a longer time period, without slowing down deployments. the work / load over a longer time period, without slowing down deployments.
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