Benjamin Duffield created ARROW-2307:
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Summary: Unable to read arrow stream containing 0 record batches
using pyarrow
Key: ARROW-2307
URL: https://issues.apache.org/jira/browse/ARROW-2307
Project: Apache Arrow
Issue Type: Bug
Components: C, Python
Affects Versions: 0.8.0
Reporter: Benjamin Duffield
Using java arrow I'm creating an arrow stream, using the stream writer.
Sometimes I don't have anything to serialize, and so I don't write any record
batches. My arrow stream thus consists of just a schema message.
{code:java}
<SCHEMA>
<EOS [optional]: int32>
{code}
I am able to deserialize this arrow stream correctly using the java stream
reader, but when reading it with python I instead hit an error
{code}
import pyarrow as pa
# ...
reader = pa.open_stream(stream)
df = reader.read_all().to_pandas()
{code}
produces
{code}
File "ipc.pxi", line 307, in pyarrow.lib._RecordBatchReader.read_all
File "error.pxi", line 77, in pyarrow.lib.check_status
ArrowInvalid: Must pass at least one record batch
{code}
i.e. we're hitting the check in
https://github.com/apache/arrow/blob/apache-arrow-0.8.0/cpp/src/arrow/table.cc#L284
The workaround we're currently using is to always ensure we serialize at least
one record batch, even if it's empty. However, I think it would be nice to
either support a stream without record batches or explicitly disallow this and
then match behaviour in java.
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