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The "Hive/JoinOptimization" page has been changed by LiyinTang. http://wiki.apache.org/hadoop/Hive/JoinOptimization?action=diff&rev1=8&rev2=9 -------------------------------------------------- In this case, the query processor will launch the original Common Join task as a Backup Task to run, which is totally transparent to user. The basic idea is shown as Fig 7. == 2.4 Performance Evaluation == + Here are some performance comparison results. All the benchmark queries here can be converted into Map Join. + '''Table 2: The Comparison between the previous join with the new optimized join''' + + ''' {{attachment:fig8.jpg}} ''' + + For the previous common join, the experiment only calculates the average time of map reduce task execution time. Because job finish time will include the job scheduling overhead. Sometimes it will wait for some time to start to run the job in the cluster. Also for the new optimized common join, the experiment only adds up the average time of local task execution time with the average time of map reduce execution time. So both of the results should avoid the job scheduling overhead. + + From the result, if the new common join can be converted into map join, it will get 57% ~163 % performance improvement. +
