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Posted to mapreduce-issues@hadoop.apache.org by "Lijie Xu (JIRA)" <ji...@apache.org> on 2012/12/17 03:54:12 UTC
[jira] [Created] (MAPREDUCE-4882) Error in estimating the length of
the output file in Spill Phase
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.
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