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https://issues.apache.org/jira/browse/TEZ-2198?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14360173#comment-14360173
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Gopal V commented on TEZ-2198:
------------------------------
That exact update means that a clear recommendation can be made on whether to
use this optimization or not by simply checking the ADDITIONAL_SPILL_COUNT &
once it is active ADDITIONAL_SPILL_COUNT will always be zero.
That makes it easy to check whether pipelined-shuffle is active & to predict
whether it adds any benefit for a given case.
> Fix sorter spill counts
> -----------------------
>
> Key: TEZ-2198
> URL: https://issues.apache.org/jira/browse/TEZ-2198
> Project: Apache Tez
> Issue Type: Improvement
> Reporter: Rajesh Balamohan
>
> Prior to pipelined shuffle, tez merged all spilled data into a single file.
> This ended up creating one index file and one output file. In this context,
> TaskCounter.ADDITIONAL_SPILL_COUNT was referred as the number of additional
> spills and there was no counter needed to track the number of merges.
> With pipelined shuffle, there is no final merge and ADDITIONAL_SPILL_COUNT
> would be misleading, as these spills are direct output files which are
> consumed by the consumers.
> It would be good to have the following
> - ADDITIONAL_SPILL_COUNT: represents the spills that are needed by the task
> to generate the final merged output
> - TOTAL_SPILLS: represents the total number of shuffle directories (index +
> output files) that got created at the end of processing.
> For e.g, Assume sorter generated 5 spills in an attempt
> Without pipelining:
> ==============
> ADDITIONAL_SPILL_COUNT = 5 <-- Additional spills involved in sorting
> TOTAL_SPILLS = 1 <-- Final merged output
> With pipelining:
> ============
> ADDITIONAL_SPILL_COUNT = 5 <-- Additional spills involved in sorting
> TOTAL_SPILLS = 0 <--- No final output
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