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https://issues.apache.org/jira/browse/PIG-2573?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13225676#comment-13225676
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Bill Graham commented on PIG-2573:
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Another approach that would be backward compatible would be to introduce an new
interface that a LoadFunc can implement to advertise that it supports load
statistics, like input size. Something similar to how StoreFuncs include a
number of optional interfaces.
Also, should we think more broadly being able to return other info besides just
total input bytes? Like we could instead return a new LoadStats object (or the
InputStats class) that could encapsulate more than just the input size. Things
like input size, records read, etc? It would be a move towards pushing stats
collection into the loaders and store funcs.
> Automagically setting parallelism based on input file size does not work with
> HCatalog
> --------------------------------------------------------------------------------------
>
> Key: PIG-2573
> URL: https://issues.apache.org/jira/browse/PIG-2573
> Project: Pig
> Issue Type: Bug
> Reporter: Travis Crawford
> Assignee: Travis Crawford
> Attachments: PIG-2573_move_getinputbytes_to_loadfunc.diff
>
>
> PIG-2334 was helpful in understanding this issue. Short version is input file
> size is only computed if the path begins with a whitelisted prefix, currently:
> * /
> * hdfs:
> * file:
> * s3n:
> As HCatalog locations use the form {{dbname.tablename}} the input file size
> is not computed, and the size-based parallelism optimization breaks.
> DETAILS:
> I discovered this issue comparing two runs on the same script, one loading
> regular HDFS paths, and one with HCatalog db.table names. I just happened to
> notice the "Setting number of reducers" line difference.
> {code:title=Loading HDFS files reducers is set to 99}
> 2012-03-08 01:33:56,522 [main] INFO
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.JobControlCompiler
> - BytesPerReducer=1000000000 maxReducers=999 totalInputFileSize=98406674162
> 2012-03-08 01:33:56,522 [main] INFO
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.JobControlCompiler
> - Neither PARALLEL nor default parallelism is set for this job. Setting
> number of reducers to 99
> {code}
> {code:title=Loading with an HCatalog db.table name}
> 2012-03-08 01:06:02,283 [main] INFO
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.JobControlCompiler
> - BytesPerReducer=1000000000 maxReducers=999 totalInputFileSize=0
> 2012-03-08 01:06:02,283 [main] INFO
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.JobControlCompiler
> - Neither PARALLEL nor default parallelism is set for this job. Setting
> number of reducers to 1
> {code}
> Possible fix: Pig should just ask the loader for the size of its inputs
> rather than special-casing certain location types.
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