[jira] [Created] (ARROW-5916) [C++] Allow RecordBatch.length to be less than array lengths

["John Muehlhausen (JIRA)" <ji...@apache.org>]

John Muehlhausen created ARROW-5916:
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             Summary: [C++] Allow RecordBatch.length to be less than array lengths
                 Key: ARROW-5916
                 URL: https://issues.apache.org/jira/browse/ARROW-5916
             Project: Apache Arrow
          Issue Type: New Feature
            Reporter: John Muehlhausen
         Attachments: test.arrow_ipc

0.13 ignored RecordBatch.length.  0.14 requires that RecordBatch.length and array length be equal.  As per [https://lists.apache.org/thread.html/2692dd8fe09c92aa313bded2f4c2d4240b9ef75a8604ec214eb02571@%3Cdev.arrow.apache.org%3E] , we discussed changing this so that RecordBatch.length can be [0,array length].

 If RecordBatch.length is less than array length, the reader should ignore the portion of the array(s) beyond RecordBatch.length.  This will allow partially populated batches to be read in scenarios identified in the above discussion.

{code:c++}
  Status GetFieldMetadata(int field_index, ArrayData* out) {
    auto nodes = metadata_->nodes();
    // pop off a field
    if (field_index >= static_cast<int>(nodes->size())) {
      return Status::Invalid("Ran out of field metadata, likely malformed");
    }
    const flatbuf::FieldNode* node = nodes->Get(field_index);

*    //out->length = node->length();*
*    out->length = metadata_->length();*
    out->null_count = node->null_count();
    out->offset = 0;
    return Status::OK();
  }
{code}

Attached is a test IPC File containing a batch with length 1, array length 3.



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