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Message Posted: Wed, 19 Nov 2008 @ 21:00:18 GMT
| Subj: || || Re: Stats collection on Index Column |
| From: || || Ramchandran, Janardhan |
| ||In fact I thought that collecting stats on UPI is also not required as it is always ONE AMP operation. But again, sometimes EXPLAIN shows
the difference like "LOW CONFIDENCE" or "HIGH CONFIDENCE".|| |
This difference your getting has "LOW CONFIDENCE" or "HIGH CONFIDENCE" because you have both index and stats gather on that column, but it in
performance it wont have the difference as it will go for the same hashing technique for the UPI and USI whether it have stats or not. So it not
that much worth able of collecting stats on the UPI or USI.
Note:- Optimizer will give "HIGH CONFIDENCE" in the explain when it uses both the index and stats for that step.
Thanks & regards