full table scan cheaper than index??

Hi.

I've got a serious problem: Yesterday I found out that some queries to a table were very slow, so I gave the "analyze"-command (estimate) to get new information about the data.
Now the optimizer seems to be completely nuts, it doesn't use any index at all!
"Set autotrace on" tells me that the cost of using an index is much higher
than a full table scan.

The database (Oracle 7.3.4) runs in "CHOOSE"-Mode, so it uses cost-based analysis.
I used "analyze table xxx estimate statistics sample 10 percent;" and another
"analyze"-command for the index to be used didn't change oracle's behaviour.
Even deleting the analysis-data (by typing "analyze table xxx delete statistics") didn't help.

Please help me, for I don't see where I think in the wrong direction.

Thanks in advance,
Jan Received on Thu Jul 12 2001 - 06:58:55 CDT