Re: HOT is applied

On 9/21/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>
>
> but control never gets that far because neither xmin nor xmax is
> committed yet. We could fix that, probably, by considering the
> xmin=xmax case in the xmin-in-progress case further up; but the
> HEAP_UPDATED exclusion is still a problem. Still, it seems like this
> is leaving some money on the table when you think about pruning a HOT
> chain. Can we improve on it easily?
>
>
May be we can, but it would get a bit tricky. There might be a transaction
looking at the first tuple in the chain and waiting for this
(inserting-deleting)
transaction to finish. If the waiting transaction is running in READ
COMMITTED
mode, it would then follow the update chain. Removing any intermediate
tuples without fixing the previous tuple's xmax/ctid (or redirected line
pointer)
would be tricky.

Thanks,
Pavan

--
Pavan Deolasee
EnterpriseDB http://www.enterprisedb.com