Kevin Grittner <kgrittn@ymail.com> writes:
> What this patch does is add a GUC call old_snapshot_threshold. It
> defaults to -1, which leaves behavior matching unpatched code.
> Above that it allows tuples to be vacuumed away after the number of
> transaction IDs specified by the GUC have been consumed.
TBH, I'm not sure why we'd wish to emulate Oracle's single worst
operational feature.
> Unlike the other patch, this one is more at the "proof of concept"
> phase, because it requires support in the heap and each index AM to
> work correctly; so far I have only had time to cover the heap and
> btree indexes.
But, having said that, why would the index AMs care? Seems like what
you are describing should be strictly a matter for VACUUM's removal
rules. If we're going to have something as ugly as this, I would much
rather it had a very small code footprint.
regards, tom lane