Skew Handling Algorithms

• Hybrid Hash
• Simple Range Partitioning

  
  		 * Sample Build relation
  
  		 * Use samples to compute approx
  
  
  partitioning vector
  
  		 * Redistribute Build relation using 
  
  approx partitioning vector
  
  		 * Build in-memory hash table. 
  
  Overflow tuples put into buckets 
  
  such that each bucket fits in memory 
  		 * Redistribute Probe relation 
  
  using the same partitioning vector
  
  		 * For each tuple of the probe 
  
  relation probe the in-memory hash table
  
  
  outputting a join result for each match 
   
  
  

• Weighted Range Partitioning

  
  		 * Use weighted partitions and 
  
  Subset-Replicate
  

• Virtual Processor Partitioning - Round Robin

  
  		 * No. of Virtual Procs 
  		 = Multiple of No. Real procs 
  

• Virtual Processor Partitioning - Processor Scheduling