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slow running query when update stats hasn't run

Posted on 2011-02-11
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Last Modified: 2012-05-11
     Hi, I have a stor proc that takes normally 2 mins to run, it's loading data into a Type 2 dimension so its doing compares.  The data is about half a million rows a day.  It seems to take 2 mins to run after I have run update stats.  When I haven't ran update stats for the day, it takes 3 hours to run.  This stor proc is part of an etl process, so I don't want to put the update stats in the middle of the package, but I do need it to take its normal time to run (2 min) .  Any suggestions how I can get this to work effciently?
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Question by:elucero
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Expert Comment

by:dwkor
ID: 34874981
Compare the plans in both cases and try to tune query with the hints and/or plan guide.
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by:MohammedU
ID: 34876204
Is Auto Update Stats is on/enabled? If not enable it and see if it improves.

You can run the updatestats as different step before etl runs...
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by:TempDBA
ID: 34878423
Elucero,
      Did you try for auto update option as Mohammed suggested? Try it out. This must help solve your problem.
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by:elucero
ID: 34880194
Its already turned on.  I can see its really slow when I'm doing an insert into the tbl that has a lot of data, we load about half a million rows a day.  This tbl also has an index on it which is why I'm having this issue.  I'm going to drop the index on the tbl and load it.  Then I'm going to make a working tbl with the index on it and load the daily data into that so I can push it to the mart.  Which would be faster for the working tbl, loading the data with the index already there or dropping and recreating the index when loading?  
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by:elucero
ID: 34880202
Isn't there a way I can run a partial updates stats?  Can I run it on just one tbl?
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Anthony Perkins earned 500 total points
ID: 34880284
>>Can I run it on just one tbl?<<
Of course. You can do it this way:
UPDATE STATISTICS YourTableNameGoesHere
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by:TempDBA
ID: 34894310
And about index thing, if there are lots of inserts happening daily, you can setup a reorganize\rebuild index job to be run daily during off hours.
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Author Comment

by:elucero
ID: 34897387
I got it to work, I took the index off the main tbl the data is inserted into daily (so of course it loads fast again).  I then made a working tbl with the index and loaded just the day data into it to load the dim.  Before I load the working tbl I truncate it and run an update stats against it.  I got the process down to 30 secs.  What is more efficient, running an update stats against the tbl or rebuilding the index?  And why do I need to do either or?  Why does this happen?
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by:Anthony Perkins
ID: 34903322
It sounds like the query is not getting the appropriate plan.  But without knowing any more details
I can only guess.
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by:elucero
ID: 35002967
what do you mean by appropriate plan?
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by:Anthony Perkins
ID: 35038804
>>what do you mean by appropriate plan? <<
The SQL plan that the QO uses in order to optimize the query.
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