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Chris Douglas commented on MAPREDUCE-64: ---------------------------------------- I was working on a patch, but got pulled into other things. It's close enough for me to finish if I can find some time in the next couple weeks. > Map-side sort is hampered by io.sort.record.percent > --------------------------------------------------- > > Key: MAPREDUCE-64 > URL: https://issues.apache.org/jira/browse/MAPREDUCE-64 > Project: Hadoop Map/Reduce > Issue Type: Bug > Reporter: Arun C Murthy > > Currently io.sort.record.percent is a fairly obscure, per-job configurable, > expert-level parameter which controls how much accounting space is available > for records in the map-side sort buffer (io.sort.mb). Typically values for > io.sort.mb (100) and io.sort.record.percent (0.05) imply that we can store > ~350,000 records in the buffer before necessitating a sort/combine/spill. > However for many applications which deal with small records e.g. the > world-famous wordcount and it's family this implies we can only use 5-10% of > io.sort.mb i.e. (5-10M) before we spill inspite of having _much_ more memory > available in the sort-buffer. The word-count for e.g. results in ~12 spills > (given hdfs block size of 64M). The presence of a combiner exacerbates the > problem by piling serialization/deserialization of records too... > Sure, jobs can configure io.sort.record.percent, but it's tedious and > obscure; we really can do better by getting the framework to automagically > pick it by using all available memory (upto io.sort.mb) for either the data > or accounting. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.