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https://issues.apache.org/jira/browse/TEZ-1228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14044970#comment-14044970
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Siddharth Seth commented on TEZ-1228:
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Looks good, reducing the amount of data sent over the wire would be really good.
Couple of questions - mainly future enhancements.
- Do we need a mechanism to skip keys. e.g. A key is read and doesn't match
whatever criteria the processor requires - would be useful to be able to skip
directly to the next key rather than having to read all values. Likely requires
an index somewhere - so that could add unnecessary overhead.
- Do we want a version optimized for cases where the key and value length are
fixed (Int for example), or is this not seen very often.
> Prototype IFile : Define a memory & merge optimized vertex-intermediate file
> format for Tez
> -------------------------------------------------------------------------------------------
>
> Key: TEZ-1228
> URL: https://issues.apache.org/jira/browse/TEZ-1228
> Project: Apache Tez
> Issue Type: Improvement
> Reporter: Rajesh Balamohan
> Labels: perfomance
> Attachments: TEZ-1228-IFile.pdf
>
>
> The current vertex-intermediate format used all across Tez is a flat file of
> variable length k,v pairs. For a significant number of use-cases, in
> particular the sorted output phase, a large number of consecutive identical
> keys are found within the same stream. The IFile format ends up writing each
> key out fully into the stream to generate (K,V) pairs instead of ordering it
> into a more efficient K, {V1, .. Vn} list.
> This duplication of key data needs larger buffers to hold in memory and
> requires comparison between keys known to be identical while doing a merge
> sort.
> This bug tracks the building of a prototype IFile format which is optimized
> for lower uncompressed sizes within memory buffers and less compute intensive
> to perform merge sorts during the reducer phase.
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