false would be "expired", this is called "expire" because it is a timestamp, it's the epoch time when the item expires. The worker presumably finishes before that time and if it does then the item is deleted. So, if any item has a nonzero expires in the past then it needs to be reset to 0 so it can be retried.

Only in databases that have no Boolean type.

Sometimes it's an artifact of the orm mapping.

So that you don't need a separate column for an associated datum?