Automagically setting parallelism based on input file size does not work with
HCatalog
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Key: PIG-2573
URL: https://issues.apache.org/jira/browse/PIG-2573
Project: Pig
Issue Type: Bug
Reporter: Travis Crawford
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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