宿荣全 created SPARK-4734:
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             Summary: limit the file Dstream size for each batch
                 Key: SPARK-4734
                 URL: https://issues.apache.org/jira/browse/SPARK-4734
             Project: Spark
          Issue Type: New Feature
          Components: Streaming
            Reporter: 宿荣全
            Priority: Minor


Streaming scan new files form the HDFS and process those files in each batch 
process.Current streaming exist some problems:
1.When the number of files is very large(the count size of those files is very 
large) in some batch segement.The processing time required will become very 
long.The processing time maybe over slideDuration time.Eventually lead to 
dispatch the next batch process is delay.
2.when the size of total file Dstream  is very large in one batch,those  
dstream data do shuffle after memory will be n times increasing occupation,app 
will be slow or even terminated by operating system.

So if we set a upper limit value of input data for each batch to control the 
batch process time,the job dispatch delay and the process delay wil be 
alleviated.

modification:
Add a new parameter "spark.streaming.segmentSizeThreshold" in InputDStream 
(input data base class).the size of each batch process segments  will be set in 
this parameter from [spark-defaults.conf.template] or setting in source.
all implements class of InputDStream will do corresponding action be aimed at 
the segmentSizeThreshold.
This patch is a modification about FileInputDStream ,so when find new files     
 ,put those files's name and size in a queue and take elements package to a 
batch data with totail size < segmentSizeThreshold  in FileInputDStream.Please 
look source about detailed logic.



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