[jira] [Updated] (ARROW-1692) [Python, Java] UnionArray round trip not working

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

     [ https://issues.apache.org/jira/browse/ARROW-1692?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wes McKinney updated ARROW-1692:
--------------------------------
    Fix Version/s:     (was: 0.9.0)
                   0.10.0

> [Python, Java] UnionArray round trip not working
> ------------------------------------------------
>
>                 Key: ARROW-1692
>                 URL: https://issues.apache.org/jira/browse/ARROW-1692
>             Project: Apache Arrow
>          Issue Type: Bug
>            Reporter: Philipp Moritz
>            Priority: Major
>             Fix For: 0.10.0
>
>         Attachments: union_array.arrow
>
>
> I'm currently working on making pyarrow.serialization data available from the Java side, one problem I was running into is that it seems the Java implementation cannot read UnionArrays generated from C++. To make this easily reproducible I created a clean Python implementation for creating UnionArrays: https://github.com/apache/arrow/pull/1216
> The data is generated with the following script:
> {code}
> import pyarrow as pa
> binary = pa.array([b'a', b'b', b'c', b'd'], type='binary')
> int64 = pa.array([1, 2, 3], type='int64')
> types = pa.array([0, 1, 0, 0, 1, 1, 0], type='int8')
> value_offsets = pa.array([0, 0, 2, 1, 1, 2, 3], type='int32')
> result = pa.UnionArray.from_arrays([binary, int64], types, value_offsets)
> batch = pa.RecordBatch.from_arrays([result], ["test"])
> sink = pa.BufferOutputStream()
> writer = pa.RecordBatchStreamWriter(sink, batch.schema)
> writer.write_batch(batch)
> sink.close()
> b = sink.get_result()
> with open("union_array.arrow", "wb") as f:
>     f.write(b)
> # Sanity check: Read the batch in again
> with open("union_array.arrow", "rb") as f:
>     b = f.read()
>     reader = pa.RecordBatchStreamReader(pa.BufferReader(b))
> batch = reader.read_next_batch()
> print("union array is", batch.column(0))
> {code}
> I attached the file generated by that script. Then when I run the following code in Java:
> {code}
> RootAllocator allocator = new RootAllocator(1000000000);
> ByteArrayInputStream in = new ByteArrayInputStream(Files.readAllBytes(Paths.get("union_array.arrow")));
> ArrowStreamReader reader = new ArrowStreamReader(in, allocator);
> reader.loadNextBatch()
> {code}
> I get the following error:
> {code}
> |  java.lang.IllegalArgumentException thrown: Could not load buffers for field test: Union(Sparse, [22, 5])<0: Binary, 1: Int(64, true)>. error message: can not truncate buffer to a larger size 7: 0
> |        at VectorLoader.loadBuffers (VectorLoader.java:83)
> |        at VectorLoader.load (VectorLoader.java:62)
> |        at ArrowReader$1.visit (ArrowReader.java:125)
> |        at ArrowReader$1.visit (ArrowReader.java:111)
> |        at ArrowRecordBatch.accepts (ArrowRecordBatch.java:128)
> |        at ArrowReader.loadNextBatch (ArrowReader.java:137)
> |        at (#7:1)
> {code}
> It seems like Java is not picking up that the UnionArray is Dense instead of Sparse. After changing the default in java/vector/src/main/codegen/templates/UnionVector.java from Sparse to Dense, I get this:
> {code}
> jshell> reader.getVectorSchemaRoot().getSchema()
> $9 ==> Schema<list: Union(Dense, [0])<: Struct<list: List<item: Union(Dense, [0])<: Int(64, true)>>>>>
> {code}
> but then reading doesn't work:
> {code}
> jshell> reader.loadNextBatch()
> |  java.lang.IllegalArgumentException thrown: Could not load buffers for field list: Union(Dense, [1])<: Struct<list: List<$data$: Union(Dense, [5])<: Int(64, true)>>>>. error message: can not truncate buffer to a larger size 1: 0
> |        at VectorLoader.loadBuffers (VectorLoader.java:83)
> |        at VectorLoader.load (VectorLoader.java:62)
> |        at ArrowReader$1.visit (ArrowReader.java:125)
> |        at ArrowReader$1.visit (ArrowReader.java:111)
> |        at ArrowRecordBatch.accepts (ArrowRecordBatch.java:128)
> |        at ArrowReader.loadNextBatch (ArrowReader.java:137)
> |        at (#8:1)
> {code}
> Any help with this is appreciated!



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