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

• Type: New Feature
• Status: Closed
• Priority: Minor
• Resolution: Later
• Component/s: C++
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/22326
• Assignee: Unassigned
• Reporter: John Muehlhausen
• Created: 12/Jul/19 04:34
• Updated: 11/Jan/23 07:43
• Resolved: 25/May/20 15:22

Description

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.

  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();
  }

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

Issue Links

• links to: GitHub Pull Request #5663