Virtual Processor Partitioning

• Eg. Consider two 10000 tuple relations in which the join attribute 1 appears 1000 times in each relation and all other attribute values appear only once.
• Dividing over 10 processors using equal sized ranged partitioning will cause both relations to map their 1000 tuples each with 1 as the join attribute value to P0 thus causing it generate 1000000 tuples.
• This is an example of severe join product skew.
• The solution lies in choosing many more partitions than there are processors. This is known as Virtual Processor Partitioning.
  
  
  
• In the Eg we could use 100 virtual processors each with 100 buckets (subranges). Now, there would be 100 1's in each of 10 virtual processors.
• Map these virtual processors to the 10 (different) real processors in a load balanced manner.