Lijie Xu created MAPREDUCE-4882: ----------------------------------- Summary: Error in estimating the length of the output file in Spill Phase Key: MAPREDUCE-4882 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4882 Project: Hadoop Map/Reduce Issue Type: Bug Affects Versions: 1.0.3, 0.20.2 Environment: Any Environment Reporter: Lijie Xu
The sortAndSpill() method in MapTask.java has an error in estimating the length of the output file. The "long size" should be "(bufvoid - bufstart) + bufend" not "(bufvoid - bufend) + bufstart" when "bufend < bufstart". Here is the original code in MapTask.java. private void sortAndSpill() throws IOException, ClassNotFoundException, InterruptedException { //approximate the length of the output file to be the length of the //buffer + header lengths for the partitions long size = (bufend >= bufstart ? bufend - bufstart : (bufvoid - bufend) + bufstart) + partitions * APPROX_HEADER_LENGTH; FSDataOutputStream out = null; ------------------------------------------------------------------------------ I had a test on "TeraSort". A snippet from mapper's log is as follows: MapTask: Spilling map output: record full = true MapTask: bufstart = 157286200; bufend = 10485460; bufvoid = 199229440 MapTask: kvstart = 262142; kvend = 131069; length = 655360 MapTask: Finished spill 3 In this occasioin, Spill Bytes should be (199229440 - 157286200) + 10485460 = 52428700 (52 MB) because the number of spilled records is 524287 and each record costs 100B. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira