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HateOra 17 posts Joined 10/13
04 Feb 2016
Unstable explain plan

We have observed weird behavior in the Teradata environment , Basically some of the SQLs suddenly starts running slow and when checked and compared to the previous explain plan for which it ran with optimal efficiency , there was deviation in the number of steps and even the plan was slightly different.
 Did anyone ever faced similar situation? 

ulrich 816 posts Joined 09/09
04 Feb 2016

Usualy you find this kind of behaviour in case of missing / stale stats.
And the cost based optimizer might decide to chose a different plan in case the demographics change. To an extreme one single additional row might change a plan...

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