RE: Statistical sampling and representative stats collection

We have a Y/N (yes/no) "processing flag" column on a very large table. As an alternative to a bitmapped index, we changed the code to manipulate Y/null values because < 0.1% of values are 'Y' and the others are null. The resulting index is quite small but we do rebuild it periodically. This has worked quite well for us.

Steve Orr
Bozeman, MT

-----Original Message-----
Sent: Wednesday, May 29, 2002 7:09 AM
To: Multiple recipients of list ORACLE-L

Have used them on a for all indexed columns basis and they make a massive difference on heavily skewed data - particularly a sort of waiting to be processed flag which only has about 5 distinct values but the ones we want to pick will make up only about 0.01%.

Haven't used them on all columns as we don't often filter on non-indexed columns.

Iain Nicoll

-----Original Message-----
Sent: Wednesday, May 29, 2002 12:59 PM
To: Multiple recipients of list ORACLE-L

>
> Based on the scarcity of previous responses to emails on this list,
> it seems that histograms are not that widely used throughout the
> industry. I'm not sure why.

I've used them in the past, but only in very specific instances and certainly not for all tables/columns. Sometimes just 1 or 2, sometimes 15 or 20. And only in those cases where needed.

>
> Cherie Machler
> Oracle DBA
> Gelco Information Network

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