[HADOOP-1535] Wrong comparator used to merge files in Reduce phase

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.12.3, 0.13.0
• Fix Version/s: 0.14.0
• Assignee: Vivek Ratan
• Reporter: Vivek Ratan
• Created: 27/Jun/07 04:56
• Updated: 08/Jul/09 16:52
• Resolved: 12/Jul/07 16:40

Description

As per the fix for HADOOP-485, we allow users to optionally provide a different comparator to group values when calling the user's Reduce function. Devaraj and I were looking at the code yesterday and we found that in ReduceTask.java, we use the user-supplied comparator to merge the output files from the Map tasks (we use the user-supplied comparator when creating a new SequenceFile.Sorter object). This is incorrect as the comparator used to merge Map output files should be the same as that used to create those files in the Map phase. The user-supplied comparator for grouping values should be used only in the iterator passed to the user's Reduce function (which is done correctly in the code).