Currently, the DB migrations guide says that "you must" use non-blocking
operations (such as CREATE INDEX CONCURRENTLY), always.
But this does not make sense in cases of empty tables and leads to
splitting the work to multiple non-atomic
(with disable_ddl_transaction!) DB migrations.
To follow KISS principle, to have fewer DB migrations steps,
to have them atomic when it's possible and simplify deployment
and troubleshooting, the following exceptions were added
to the doc:
- index creation,
- index dropping,
- defining an FK,
- adding a column with DEFAULT,
- Add a new guideline regarding the file location of background
migrations
- Add a new section about execution timing guidelines for all different
kinds of migrations
