[jira] [Created] (ARROW-399) [Java] ListVector.loadFieldBuffers ignores the ArrowFieldNode length metadata

["Wes McKinney (JIRA)" <ji...@apache.org>]

Wes McKinney created ARROW-399:
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             Summary: [Java] ListVector.loadFieldBuffers ignores the ArrowFieldNode length metadata
                 Key: ARROW-399
                 URL: https://issues.apache.org/jira/browse/ARROW-399
             Project: Apache Arrow
          Issue Type: Bug
          Components: Java - Vectors
            Reporter: Wes McKinney
            Priority: Blocker
         Attachments: list_error.json

Discovered this during integration testing. Because Arrow-C++ writes buffers padded to 64 bytes, they may appear larger to the Java library than they need to be. In ListVector.loadFieldBuffers, the ArrowFieldNode is never used:

{code|language=java}
  @Override
  public void loadFieldBuffers(ArrowFieldNode fieldNode, List<ArrowBuf> ownBuffers) {
    BaseDataValueVector.load(getFieldInnerVectors(), ownBuffers);
  }
{code}

The value count of the resulting ListVector is thus inferred from the size of the offsets buffer. In the case of a length-7 vector in C++, the size of the offsets buffer is exactly 64 bytes (padding for SIMD) -- Java infers from 64 bytes that the value count is 15 (64 / 4 - 1), and the integration test fails.



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