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From "Thejas M Nair (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-1472) Optimize serialization/deserialization between Map and Reduce and between MR jobs
Date Mon, 12 Jul 2010 17:40:49 GMT

    [ https://issues.apache.org/jira/browse/PIG-1472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12887441#action_12887441
] 

Thejas M Nair commented on PIG-1472:
------------------------------------

bq. 1. The following code are never used in BinStorage and InterStorage, should be removed.

I will remove that.

bq. 3. Seems InterStorage is a replacement for BinStorage, why do we make it private? Shall
we encourage user use InterStorage in the place of BinStorage, and make BinStorage deprecate?
In future, we are likely to find better ways to serialize data between MR jobs of a pig query.
ie the InterSedes serialization format is likely to change, and the change is not likely to
be compatible with its old format. So it will not be suitable for storing persistent data.

This replaces BinStorage only for its use within pig. Since BinStorage is used in pig queries
and it should be easy to maintain the code, I think we don't have to deprecate BinStorage.



> Optimize serialization/deserialization between Map and Reduce and between MR jobs
> ---------------------------------------------------------------------------------
>
>                 Key: PIG-1472
>                 URL: https://issues.apache.org/jira/browse/PIG-1472
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: 0.8.0
>            Reporter: Thejas M Nair
>            Assignee: Thejas M Nair
>             Fix For: 0.8.0
>
>         Attachments: PIG-1472.2.patch, PIG-1472.3.patch, PIG-1472.patch
>
>
> In certain types of pig queries most of the execution time is spent in serializing/deserializing
(sedes) records between Map and Reduce and between MR jobs. 
> For example, if PigMix queries are modified to specify types for all the fields in the
load statement schema, some of the queries (L2,L3,L9, L10 in pigmix v1) that have records
with bags and maps being transmitted across map or reduce boundaries run a lot longer (runtime
increase of few times has been seen.
> There are a few optimizations that have shown to improve the performance of sedes in
my tests -
> 1. Use smaller number of bytes to store length of the column . For example if a bytearray
is smaller than 255 bytes , a byte can be used to store the length instead of the integer
that is currently used.
> 2. Instead of custom code to do sedes on Strings, use DataOutput.writeUTF and DataInput.readUTF.
 This reduces the cost of serialization by more than 1/2. 
> Zebra and BinStorage are known to use DefaultTuple sedes functionality. The serialization
format that these loaders use cannot change, so after the optimization their format is going
to be different from the format used between M/R boundaries.

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