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Message Posted: Fri, 11 Feb 2005 @ 17:28:12 GMT


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Subj:		Re: Query Length Time Increase

From:		Dieter Noeth

Craig Ferry wrote:

I have a strange problem. I have a query that I am running. If I add another where clause, the response time goes from 8 to 22 minutes. I know this is rather vague, but I have included the query and explain plans below (I can send the ddl statements if anyone is really interested). Any suggestions as to why adding an additional limiting factor on the data would increase query response time? I would have thought just the opposite. Statistics are collected on all the columns referenced on all the tables.

Are you shure about statistics? There's a lot of low or no confidence...

If you run a current patch level in V2R5+ submit a

"diagnostic helpstats on for session;"

to find out about missing stats.

If you explain a query it adds a new section to the end of explain text:

     BEGIN RECOMMENDED STATS ->
...
     <- END RECOMMENDED STATS

But don't worry too much about it, the optimizer usually recommends stats on almost every column used (and always tells about (HighConf) as resulting confidence level, even if it's not true)

Dieter


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