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,
These are data columns that store runtime configuration
of build needed to execute it on runner and within pipeline.
The definition of this data is that once used, and when no longer
needed (due to retry capability) they can be freely removed.
They use `jsonb` on PostgreSQL, and `text` on MySQL (due to lacking
support for json datatype on old enough version).
Index creation does not have an effect if the index is present already.
Index removal does not have an affect if the index is not present.
This helps to avoid patterns like this in migrations:
```
if index_exists?(...)
remove_concurrent_index(...)
end
```
Starting with GitLab 9.1.0 we will no longer allow downtime migrations
unless absolutely necessary. This commit updates the various developer
guides and adds code that is necessary to make zero downtime migrations
less painful.
These new checks can be used to check if migrations require downtime or
not (as tagged by their authors). In CI this compares the current branch
with master so migrations added by merge requests are automatically
verified.
To check the migrations added since a Git reference simply run:
bundle exec rake gitlab:db:downtime_check[GIT_REF]
GitLab Bot
Evan Read
Mayra Cabrera
Valery Sizov
Marcel Amirault
Shinya Maeda
Gosia Ksionek
Kamil Trzciński
Yorick Peterse
Nikolay
Andreas Brandl
Brett Walker
Ville Skyttä
Sean McGivern
blackst0ne
Bob Van Landuyt
Robert Speicher
Nick Thomas
Drew Blessing
Drew Blessing
Chris Spicer
Rémy Coutable
Prayag Verma
Valery Sizov
Sytse Sijbrandij
Job van der Voort