#31653: PostgreSQL add constraints via NOT VALID / VALIDATE CONSTRAINT
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Reporter: Adam (Chainz) Johnson | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Migrations | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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If you read the ALTER TABLE PostgreSQL docs (
https://www.postgresql.org/docs/12/sql-altertable.html ) for `ADD
CONSTRAINT`, you'll see that it supports the `NOT VALID` option. This
prevents the constraint from being checked against all existing data,
although it does affect all inserted/updated rows. Adding a constraint
this way does not exclusively lock the whole table to check it. To promote
it to valid, the `VALIDATE CONSTRAINT` syntax can be used. This allows a
non-exclusive lock on the table to validate all existing rows. This two
step techinque allows constraints to be added to very active tables
without locking out concurrent access and thus inflicting downtime.
I suggest Django always use this form when adding foreign keys and check
constraints.
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Ticket URL: <https://code.djangoproject.com/ticket/31653>
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