RE: How many is too many

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_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] 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.

This email and any attachments are confidential and may also be privileged. If you are not the addressee, do not disclose, copy, circulate or in any other way use or rely on the information contained in this email or any attachments. If received in error, notify the sender immediately and delete this email and any attachments from your system. Emails cannot be guaranteed to be secure or error free as the message and any attachments could be intercepted, corrupted, lost, delayed, incomplete or amended. Standard Chartered PLC and its subsidiaries do not accept liability for damage caused by this email or any attachments and may monitor email traffic.

Standard Chartered PLC is incorporated in England with limited liability under company number 966425 and has its registered office at 1 Aldermanbury Square, London, EC2V 7SB.

Standard Chartered Bank ("SCB") is incorporated in England with limited liability by Royal Charter 1853, under reference ZC18. The Principal Office of SCB is situated in England at 1 Aldermanbury Square, London EC2V 7SB. In the United Kingdom, SCB is authorised and regulated by the Financial Services Authority under FSA register number 114276.

If you are receiving this email from SCB outside the UK, please click http://www.standardchartered.com/global/email_disclaimer.html to refer to the information on other jurisdictions.

--
http://www.freelists.org/webpage/oracle-l