Re: can clustering help INSERTS ?

DENNIS WILLIAMS wrote:
>
> Stephane
> You mentioned "each additional index costs about 2.5 times the cost of
> inserting into a non-indexed table". I just wanted to point out that Kevin
> Loney has done some performance tests involving the number of indexes. I
> don't know if he has published these anywhere. In a nutshell, the results
> were that a single index really hurts insert performance, and each
> additional index increases the hurt, but by a decreasing amount. The
> conclusions were:
> - If you can drop all indexes, that will really help inserts.
> - If you have one index, adding a second index will really hurt, but not
> as bad.
> - If the table already has 15 indexes, adding one more index probably
> won't be noticed.
>
> Dennis Williams
> DBA, 40%OCP
> Lifetouch, Inc.
> dwilliams_at_lifetouch.com
>

Dennis,

   I have also benched it, and what I gave are my results. Note that we totally agree in _relative_ terms. If you have 15 indexes, I estimate the cost to be about 100 + 15 * 250, so in truth at this stage the cost of an index is about 7% ...
Note also that the costs I gave are relative to the number of logical reads. I have met a number of cases when a significant increase in logical reads was hardly noticeable in terms of elapsed time.

-- 
Regards,

Stephane Faroult
Oriole Software
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Author: Stephane Faroult
  INET: sfaroult_at_oriole.com

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