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https://issues.apache.org/jira/browse/ARROW-6896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16952475#comment-16952475
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Jacques Nadeau commented on ARROW-6896:
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I disagree with the issue here. We should probably add a better description of
reference count semantics but having the container close it's children makes
sense. We depend on this functionality quite a bit.
Generally speaking, Vectors are things that shouldn't be handed around, they
should be transferred, which has clear reference management semantics. The
design was based on the [AttributeSource design
pattern|[https://lucene.apache.org/core/5_4_0/core/org/apache/lucene/util/AttributeSource.html]]
in Lucene where you create an object once and then pass many separate pieces
of data through it to minimize heap churn and pointer/reference management. I
think if you're hitting the problem you describe, you're misunderstanding the
goals of the codebase.
> [Java] Vector schema root should not share vectors
> --------------------------------------------------
>
> Key: ARROW-6896
> URL: https://issues.apache.org/jira/browse/ARROW-6896
> Project: Apache Arrow
> Issue Type: Bug
> Components: Java
> Reporter: Liya Fan
> Assignee: Liya Fan
> Priority: Major
> Labels: pull-request-available
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Vector schema root should not share vectors. Otherwise, unexpectd behavior
> would happen.
> Please note that VectorSchemaRoot is not just a container for vectors, it is
> also a resource (it implements the AutoClosable interface), and it manages
> the life cycle of its inner vectors.
> When two VectorSchemaRoots share vectors, something unexpected may happen.
> Consider the following scenario, which is frequently encountered in a SQL
> engine.
> 1. We create a batch:
> VectorSchemaRoot oldBatch = ...
> 2. We add a vector to it, which results in a new batch
> VectorSchemaRoot newBatch = oldBatch.addVector(vector);
> 3. We are done with the old batch, and release the resource
> oldBatch.close();
> 4. We continue to use the new batch, but gets an exception, because some
> inner vectors have been released by the old batch.
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