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

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

     [ https://issues.apache.org/jira/browse/ARROW-399?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wes McKinney updated ARROW-399:
-------------------------------
    Attachment: list_error.json

> [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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