[jira] [Created] (APEXMALHAR-2032) MapReduce Input format support for File Splitter

["devendra tagare (JIRA)" <ji...@apache.org>]

devendra tagare created APEXMALHAR-2032:
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             Summary: MapReduce Input format support for File Splitter
                 Key: APEXMALHAR-2032
                 URL: https://issues.apache.org/jira/browse/APEXMALHAR-2032
             Project: Apache Apex Malhar
          Issue Type: New Feature
            Reporter: devendra tagare


Extending the FileSplitter to work with InputSplit & the BlockReader to work with the RecordReader from org.apache.hadoop.mapreduce.InputSplit & org.apache.hadoop.mapreduce.RecordReader respectively.
Some more details and rationale on the approach,
InputFormat lets MR create Input Splits ie individual chunks of bytes.
The ability to correctly create these splits is determined by the Input Format itself.eg SequenceFile format or Avro.
Internally these formats are organized as a sequence of blocks.Each block can be compressed with a compression codec & it does not matter if this codec in itself is splittable.
When they are set as an Input format, the MR framework creates input splits based on the block boundaries given by the metadata object packed with the file.
Each InputFormat has a specific block definition. eg for Avro the block definition is as below,
Avro file data block consists of:
A long indicating the count of objects in this block.
A long indicating the size in bytes of the serialized objects in the current block, after any codec is applied
The serialized objects. If a codec is specified, this is compressed by that codec.
The file's 16-byte sync marker.
Thus, each block's binary data can be efficiently extracted or skipped without deserializing the contents. The combination of block size, object counts, and sync markers enable detection of corrupt blocks and help ensure data integrity.
Each map task gets an entire block to read.RecordReader is used to read the individual records for the block and generates key,val pairs.
The records could be fixed length or use a schema as in the case of parquet or Avro.
We can extend the BlockReader to work with RecordReader based on the sync markers to correctly identify & parse the individual records.
Thanks,
Dev




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