query uses function based index in DEV1 db but does NOT use it in DEV2 db

I have a query that uses function based index in DEV1 db but does NOT use it in DEV2 db. I've compared parameters db_file_multiblock_read_count and optimizer_index_cost_adj, they are identical between DEV1 and DEV2. I've gathered system stats and stats on the tables that the query is based on in DEV2. Still the query refuses to use the index in DEV2. I can use the index() hint to force it to use it but that's not an accepted way to resolve this issue. Another strange thing is: even a commented out hint would make the query to use the index. such as:

select --/*+ index(tranlogtra0_ NU_TTL_CANX) */

I am confused and wondering what else I can do? Version 11.1.0.7.0 on RHEL 5.3

Any suggestions and comments would be greatly appreciated!
-Li
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http://www.freelists.org/webpage/oracle-l Received on Wed Apr 25 2012 - 09:33:54 CDT