Types of Skew

• Attribute value skew
• Tuple placement skew
• Redistribution skew (caused by bad partitioning)
• Execution skew (causes uneven bad work distribution)
  Selectivity skew (in which all tuples are from P0 and none from P1)
• Join Product skew
  * Some join attributes are more common in both relations eg. For an Equi-join on attribute A in R and S if there are 10 a's in R.A and 10 a's in S.A then the equijoin has 10*10 a's
• Equal distribution of tuples may not be enough