RE: How many is too many
- From: "Chitale, Hemant Krishnarao" <Hemant.Chitale@xxxxxx>
- To: <veeeraman@xxxxxxxxx>
- Date: Fri, 12 Aug 2011 11:17:41 +0800
A simple calculation would be :
If the INSERT/DELETE overhead caused by the presence of 12 indexes is
12x, then the INSERT/DELETE overhead caused by the presence of 13
indexes is 13x.
Thus, the "increase" in overhead is 1/12th !
(UPDATE overhead is a function of which columns are updated relative to
which indexes hold those columns).
[By that calculation, the addition of a second index to a 1-index table
is a 100% increase in Index overhead. But, since the Index overhead
[value 'x'] itself is very low for a single index, the 100% increase is
not noticeable !]
However, this is an opportunity to review *existing* indexes.
Hemant K Chitale
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Ram Raman
Sent: Friday, August 12, 2011 4:45 AM
To: ORACLE-L
Subject: How many is too many
Listers,
I am looking at a table in our system and it has 12 indexes, we are
planning on adding another one. I am aware of the effects of having too
many indexes, but in this case adding an extra index helps a certain
query that runs slow. Other queries and most other operations against
the table are acceptable too. I see a few tables like this; is there a
number above which is considered a no-no when it comes to adding more
indexes.
PS. The tables and queries are structured in a way that seem to require
several indexes - it is a third party product.
TIA,
Ram.
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