Re: 9.2 and index only scans

Thomas Kellerer <spam_eater(at)gmx(dot)net> writes:
> Martijn van Oosterhout, 28.08.2012 10:02:
>> I'm not sure how oracle avoids the same issues:
>> - The index has no visibility information, so you can't tell if an
>> index entry refers to a row you can actually see in your session.
>> The visibility map might help here in the future.

> In Oracle an index (entry) has the information about transactional visibility.

You sure about that?

What I always understood about Oracle is that the main table (and by
implication, also the indexes) has *only* the most up-to-date version
of any row. If you want back versions, you have to go trawling for them
in the rollback segments. That approach has its pluses and minuses
compared to ours, but it doesn't seem to lead to keeping visibility info
in the index.

regards, tom lane