| From: | Chris Travers <chris(dot)travers(at)gmail(dot)com> |
|---|---|
| To: | Craig Ringer <ringerc(at)ringerc(dot)id(dot)au> |
| Cc: | Thomas Kellerer <spam_eater(at)gmx(dot)net>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: 9.2 and index only scans |
| Date: | 2012-08-28 13:55:20 |
| Message-ID: | CAKt_Zfv+Y5T2eW6t1UV2zoZRd42yKbiWCiiBBdfE2hBFN7Y1ig@mail.gmail.com |
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| Lists: | pgsql-general |
On Tue, Aug 28, 2012 at 6:04 AM, Craig Ringer <ringerc(at)ringerc(dot)id(dot)au> wrote:
> On 08/28/2012 05:51 PM, Thomas Kellerer wrote:
>
>> 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.
>>
>
> Wow. Doesn't that mean that indexes are insanely expensive to update,
> since each index (and possibly also the table its self) needs updating?
>
I was thinking of read performance. But it might be a case where the
global optimization might be worth the local cost. I don't know.
Best Wishes,
Chris Travers
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