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1958952 - ASE: Statistics from huge tables show a large skew and majority of values are in the last histogram step

Symptom

  • The last step in the histogram's Step Weight Value represents 64% of the data
     
  • Statistics  from huge tables shows a large skew for the last histogram step, even  after executing  'update statistics'
     
  • This is an example of the last 3 steps for a table that has more than 2.1 billion (2^31) rows using  1000 steps
       ...
       998 0.00000000 < "Feb 13 2009 12:00:00:000AM"
       999 0.00045268 = "Feb 13 2009 12:00:00:000AM"
       1000 0.64416260 < = "Jan 1 2099 12:00:00:000AM"
     
  •  When statistics are skewed like this the optimizer may not have the best query plan and  table scans might be used


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Environment

SAP ASE Adaptive Server Enterprise (ASE) 15.x

Product

SAP Adaptive Server Enterprise 15.7 ; Sybase Adaptive Server Enterprise 15.0 ; Sybase Adaptive Server Enterprise 15.5

Keywords

unbalanced weight , KBA , BC-SYB-ASE , Sybase ASE Database Platform (non Business Suite) , Bug Filed

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