RE: can clustering help INSERTS ?

Dennis,

Did he publish any figures? I mean, it seems common-sense that adding the first index will hurt but adding 11th index to a table won't hurt that much.

As stephane pointed out, cost of an index is 2.5 times more than the cost of insert in a non-indexed table.

So assuming cost is 1, than cost with 1 index will be 3.5 as 250% increase.

Cost with 5 indexes should be 13.5 and cost with 6 indexes will be 16 less than twenty percent increase.

Since the addition cost is constant for every index added, the percentage increase in cost (and also maybe time) will be lower and lower.

Am I right or missing something?

Regards
Naveen

-----Original Message-----
Sent: Friday, October 25, 2002 11:45 PM
To: Multiple recipients of list ORACLE-L

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

-----Original Message-----
Sent: Friday, October 25, 2002 8:04 AM
To: Multiple recipients of list ORACLE-L

Rahul wrote:
>
> List,
> i have two heavily inserted tables, the structures are same.
> currently these tables reside on separate disks, can i increase the
> performance
> of inserts if i create these tables in a cluster ? as a cluster would
force
> the rows of both the tables
> to be physically close on the disk !
>
> regards
> -rahul
>
> Ora 7.3 on AIX
>

You would also increase contention ... I'd rather try to augment the number of free lists, and, if you are lucky enough not to access your indexes in RANGE SCAN mode, to create them as REVERSE. Beware of indexes, by the way, each additional index costs about 2.5 times the cost of inserting into a non-indexed table (in terms of logical blocks).

-- 
Regards,

Stephane Faroult
Oriole Software
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