mirror of
https://github.com/matrix-org/dendrite
synced 2024-12-13 22:35:40 +01:00
109 lines
3.8 KiB
Markdown
109 lines
3.8 KiB
Markdown
## Database migrations
|
|
|
|
We use [goose](https://github.com/pressly/goose) to handle database migrations. This allows us to execute
|
|
both SQL deltas (e.g `ALTER TABLE ...`) as well as manipulate data in the database in Go using Go functions.
|
|
|
|
To run a migration, the `goose` binary in this directory needs to be built:
|
|
```
|
|
$ go build ./cmd/goose
|
|
```
|
|
|
|
This binary allows Dendrite databases to be upgraded and downgraded. Sample usage for upgrading the roomserver database:
|
|
|
|
```
|
|
# for sqlite
|
|
$ ./goose -dir roomserver/storage/sqlite3/deltas sqlite3 ./roomserver.db up
|
|
|
|
# for postgres
|
|
$ ./goose -dir roomserver/storage/postgres/deltas postgres "user=dendrite dbname=dendrite sslmode=disable" up
|
|
```
|
|
|
|
For a full list of options, including rollbacks, see https://github.com/pressly/goose or use `goose` with no args.
|
|
|
|
|
|
### Rationale
|
|
|
|
Dendrite creates tables on startup using `CREATE TABLE IF NOT EXISTS`, so you might think that we should also
|
|
apply version upgrades on startup as well. This is convenient and doesn't involve an additional binary to run
|
|
which complicates upgrades. However, combining the upgrade mechanism and the server binary makes it difficult
|
|
to handle rollbacks. Firstly, how do you specify you wish to rollback? We would have to add additional flags
|
|
to the main server binary to say "rollback to version X". Secondly, if you roll back the server binary from
|
|
version 5 to version 4, the version 4 binary doesn't know how to rollback the database from version 5 to
|
|
version 4! For these reasons, we prefer to have a separate "upgrade" binary which is run for database upgrades.
|
|
Rather than roll-our-own migration tool, we decided to use [goose](https://github.com/pressly/goose) as it supports
|
|
complex migrations in Go code in addition to just executing SQL deltas. Other alternatives like
|
|
`github.com/golang-migrate/migrate` [do not support](https://github.com/golang-migrate/migrate/issues/15) these
|
|
kinds of complex migrations.
|
|
|
|
### Adding new deltas
|
|
|
|
You can add `.sql` or `.go` files manually or you can use goose to create them for you.
|
|
|
|
If you only want to add a SQL delta then run:
|
|
|
|
```
|
|
$ ./goose -dir serverkeyapi/storage/sqlite3/deltas sqlite3 ./foo.db create new_col sql
|
|
2020/09/09 14:37:43 Created new file: serverkeyapi/storage/sqlite3/deltas/20200909143743_new_col.sql
|
|
```
|
|
|
|
In this case, the version number is `20200909143743`. The important thing is that it is always increasing.
|
|
|
|
Then add up/downgrade SQL commands to the created file which looks like:
|
|
```sql
|
|
-- +goose Up
|
|
-- +goose StatementBegin
|
|
SELECT 'up SQL query';
|
|
-- +goose StatementEnd
|
|
|
|
-- +goose Down
|
|
-- +goose StatementBegin
|
|
SELECT 'down SQL query';
|
|
-- +goose StatementEnd
|
|
|
|
```
|
|
You __must__ keep the `+goose` annotations. You'll need to repeat this process for Postgres.
|
|
|
|
For complex Go migrations:
|
|
|
|
```
|
|
$ ./goose -dir serverkeyapi/storage/sqlite3/deltas sqlite3 ./foo.db create complex_update go
|
|
2020/09/09 14:40:38 Created new file: serverkeyapi/storage/sqlite3/deltas/20200909144038_complex_update.go
|
|
```
|
|
|
|
Then modify the created `.go` file which looks like:
|
|
|
|
```go
|
|
package migrations
|
|
|
|
import (
|
|
"database/sql"
|
|
"fmt"
|
|
|
|
"github.com/pressly/goose"
|
|
)
|
|
|
|
func init() {
|
|
goose.AddMigration(upComplexUpdate, downComplexUpdate)
|
|
}
|
|
|
|
func upComplexUpdate(tx *sql.Tx) error {
|
|
// This code is executed when the migration is applied.
|
|
return nil
|
|
}
|
|
|
|
func downComplexUpdate(tx *sql.Tx) error {
|
|
// This code is executed when the migration is rolled back.
|
|
return nil
|
|
}
|
|
|
|
```
|
|
|
|
You __must__ import the package in `/cmd/goose/main.go` so `func init()` gets called.
|
|
|
|
|
|
#### Database limitations
|
|
|
|
- SQLite3 does NOT support `ALTER TABLE table_name DROP COLUMN` - you would have to rename the column or drop the table
|
|
entirely and recreate it. ([example](https://github.com/matrix-org/dendrite/blob/master/userapi/storage/accounts/sqlite3/deltas/20200929203058_is_active.sql))
|
|
|
|
More information: [sqlite.org](https://www.sqlite.org/lang_altertable.html)
|