Commit 1600a483 authored by John Hope's avatar John Hope Committed by Yannis Roussos

Add guidance for irreversible data migrations

parent e39da6a8
...@@ -132,6 +132,18 @@ test its execution using `CREATE INDEX CONCURRENTLY` in the `#database-lab` Slac ...@@ -132,6 +132,18 @@ test its execution using `CREATE INDEX CONCURRENTLY` in the `#database-lab` Slac
- This job runs migrations in a production-like environment (similar to `#database_lab`) and posts to the MR its findings (queries, runtime, size change). - This job runs migrations in a production-like environment (similar to `#database_lab`) and posts to the MR its findings (queries, runtime, size change).
- Review migration runtimes and any warnings. - Review migration runtimes and any warnings.
#### Preparation when adding data migrations
Data migrations are inherently risky. Additional actions are required to reduce the possibility
of error that would result in corruption or loss of production data.
Include in the MR description:
- If the migration itself is not reversible, details of how data changes could be reverted in the event of an incident. For example, in the case of a migration that deletes records (an operation that most of the times is not automatically revertable), how _could_ the deleted records be recovered.
- If the migration deletes data apply the label `~data-deletion`
- Concise descriptions of possible user experience impact of an error; for example, "Issues would unexpectedly go missing from Epics".
- Relevant data from the [query plans](#query-plans) that indicate the query works as expected; such as the approximate number of records that will be modified/deleted.
#### Preparation when adding or modifying queries #### Preparation when adding or modifying queries
##### Raw SQL ##### Raw SQL
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...@@ -162,6 +162,9 @@ def down ...@@ -162,6 +162,9 @@ def down
end end
``` ```
Migrations like this are inherently risky and [additional actions](database_review.md#preparation-when-adding-data-migrations)
are required when preparing the migration for review.
## Atomicity ## Atomicity
By default, migrations are single transaction. That is, a transaction is opened By default, migrations are single transaction. That is, a transaction is opened
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