Robert Nishihara created ARROW-1194:
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Summary: Trouble deserializing a pandas DataFrame from a PyArrow
buffer.
Key: ARROW-1194
URL: https://issues.apache.org/jira/browse/ARROW-1194
Project: Apache Arrow
Issue Type: Bug
Components: Python
Affects Versions: 0.5.0
Environment: Ubuntu 16.04
Python 3.6
Reporter: Robert Nishihara
I'm running into the following problem.
Suppose I create a dataframe and serialize it.
{code:language=python}
import pyarrow as pa
import pandas as pd
df = pd.DataFrame({"a": [1, 2, 3]})
record_batch = pa.RecordBatch.from_pandas(df)
{code}
It's size is 352 according to
{code:language=python}
pa.get_record_batch_size(record_batch) # This is 352.
{code}
However, if I write it using a stream_writer and then attempt to read it, the
resulting buffer has size 928.
{code:language=python}
sink = pa.BufferOutputStream()
stream_writer = pa.RecordBatchStreamWriter(sink, record_batch.schema)
stream_writer.write_batch(record_batch)
new_buf = sink.get_result()
new_buf.size # This is 928.
{code}
I'm running into this problem because I'm attempting to write the pandas
DataFrame to the Plasma object store as follows (after Plasma has been started
and a client has been created), so I need to know the size ahead of time.
{code:language=python}
data_size = pa.get_record_batch_size(record_batch)
object_id = plasma.ObjectID(np.random.bytes(20))
buf = client.create(object_id, data_size) # Note that if I replace "data_size"
by "data_size + 1000" then it works.
stream = plasma.FixedSizeBufferOutputStream(buf)
stream_writer = pa.RecordBatchStreamWriter(stream, record_batch.schema)
stream_writer.write_batch(record_batch)
{code}
The above fails because the buffer allocated in Plasma only has size 352, but
928 bytes are needed.
So my question is, am I determining the size of the record batch incorrectly?
Or could there be a bug in {code:language=python}pa.get_record_batch_size{code}
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