Haas: DO or UNDO - there is no VACUUM

PostgreSQL developer Robert Haas describes a new storage module that is under development. "We are working to build a new table storage format for PostgreSQL, which we’re calling zheap. In a zheap, whenever possible, we handle an UPDATE by moving the old row version to an undo log, and putting the new row version in the place previously occupied by the old one. If the transaction aborts, we retrieve the old row version from undo and put it back in the original location; if a concurrent transaction needs to see the old row version, it can find it in undo. [...] This means that there is no need for VACUUM, or any similar process, to scan the table looking for dead rows."

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