Optimize indexes

Question

10g. A table has 50 columns, 17 indexes, operation on this table is slow.
How to optimize these indexes? Where to find which is not used, etc.
Thanks.

Answer 1

neem wrote:
checked: all indexes has been used. how to optimize these indexes is for next step.How did you check that all the indexes had been used ?
If you've used a query against the AWR looking for execution plans that reference the index, you've made two possible mistakes.
First - the AWR only records a selection of all the SQL that has been executed, so you might decide that some indexes weren't being used when they were. (In your case, you've decided that all the indexes were used, so this doesn't apply).
Second - when the automatic stats collection job runs in 10g, it uses a simple piece of SQL that will generate an execution plan that accesses the index, so you may decide that you've used the index when the only SQL that ever uses it is the SQL that collects stats on it.
Since you don't know what the indexes are for (and "the developers created them" is not an answer to that question) then a simple first step is a quick sanity check. Look at all the index definitions to see if any of them seem to be redundant. The very first step (which may then need to be refined) is a query like:
break on index_name skip 1
column index_name, format a32
column column_name format a32
select 
     index_name, column_name
from
     user_ind_columns
where
     table_name = 'your tablename goes here'
order by
     index_name, column_position
;(This assumes you are connected as the owner of the table - if not, you will have to query dba_ind_columns and include a predicate on the table_owner column).
Post the results to the forum if you can't spot any obvious suspects:
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
"Science is more than a body of knowledge; it is a way of thinking"
Carl Sagan
To post code, statspack/AWR report, execution plans or trace files, start and end the section with the tag {noformat}{noformat} (lowercase, curly brackets, no spaces) so that the text appears in fixed format.