Simon Riggs wrote:
> CTIDs don't help with optimistic locking, though it seems they can.
>
> If you don't hold open the transaction then someone else can update the
> row. That sounds good, but because of HOT it is possible that the same
> CTID with the same PK value occupies that exact CTID value when you
> return to check it. You think row has not been updated so you perform
> your update, but it has been updated, so you overwrite previous data -
> data loss. Actually worse, sporadic data loss because of race
> conditions.
Yeah, you have to check xmin as well.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com