Enforce NOT NULL constraint on notification_status

[DilwoarH]

What

Enforce NOT NULL constraint on notification_status

Why

Without NOT NULL - we cannot create an index for notification_status column

Checked DB:

SELECT count(*)
 FROM notifications where notification_status is NULL;

Result was 0

Context

This is needed as we need to implement the following replica identity:

ALTER TABLE notifications REPLICA IDENTITY USING INDEX ix_notifications_id_status;

Without adding this index we would have to put the replica on the whole table which will keep track of old values of every column which is not needed.

[spatel033]

Notifications table only handles INSERT and UPDATE operations, PostgreSQL’s default replica identity already includes all required columns (template_id, notification_status, created_at) in the wal2json stream using our existing id primary key.
The DELETE operations are for archiving notifications to notification_history where notification_status counts must remain unchanged, so our aggregator can simply ignore all delete logs.
I think in this case we can skip this migration and it also saves write overhead on notifications table.

[risicle]

😕 the default replica identity is simply id, is it not? And as such we don't get the old values for the status field in the wal2json stream, which we need for bookkeeping so we know which field in the status table to decrement as a notification moves to another status.

I agree it's a shame this increases our write load slightly, but I don't think there's another way.

[DilwoarH]

Yeah unfortunately, only returns ID so without this index there is no other way to get the old values.

[DilwoarH]

The base branch for this has now been changed to main - this can be merge in independently

[whpearson]

Change makes sense. Shouldn't lock the notifications table.Tested locally

[risicle]

I don't understand the name of the migration

[DilwoarH]

@risicle - migrations have been split up