Yogesh Tewari created ARROW-7048:
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Summary: [Java] Support for combining multiple vectors under
VectorSchemaRoot
Key: ARROW-7048
URL: https://issues.apache.org/jira/browse/ARROW-7048
Project: Apache Arrow
Issue Type: New Feature
Components: Java
Reporter: Yogesh Tewari
Hi,
pyarrow.Table.combine_chunks provides a nice functionality of combining
multiple batch records under a single pyarrow.Table.
I am currently working on a downstream application which reads data from
BigQuery. BigQuery storage api supports data output in Arrow format but streams
data in many batches of size 1024 or less number of rows.
It would be really nice to have Arrow Java api provide this functionality under
an abstraction like VectorSchemaRoot.
After getting guidance from [~emkornfi...@gmail.com], I tried to write my own
implementation by copying data vector by vector using TransferPair's
copyValueSafe
But, unless I am missing some thing obvious, turns out it only copies one value
at a time. That means a lot of looping trying copyValueSafe millions of rows
from source vector index to target vector index. Ideally I would want to
concatenate/link the underlying buffers rather than copying one cell at a time.
Eg, if I have :
{code:java}
List<VectorSchemaRoot> batchList = new ArrayList<>();
try (ArrowStreamReader reader = new ArrowStreamReader(new
ByteArrayInputStream(out.toByteArray()), allocator)) {
Schema schema = reader.getVectorSchemaRoot().getSchema();
for (int i = 0; i < 5; i++) {
// This will be loaded with new values on every call to loadNextBatch
VectorSchemaRoot readBatch = reader.getVectorSchemaRoot();
reader.loadNextBatch();
batchList.add(readBatch);
}
}
//VectorSchemaRoot.combineChunks(batchList, newVectorSchemaRoot);{code}
A method like VectorSchemaRoot.combineChunks(List<VectorSchemaRoot>)?
I did read the VectorSchemaRoot discussion on
https://issues.apache.org/jira/browse/ARROW-6896 and am not sure if its the
right thing to use here.
PS. Feel free to update the title of this feature request to more appropriate
wordings.
Cheers,
Yogesh
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