Hi,

I am an beginner of Arrow and Plasma, I am trying to use them in my project to improve performance. 

I will slice the origin VectorSchemaRoot and get many sliced VectorSchemaRoot in my project, and then I will store these VectorSchemaRoot into Plasma and the objectIds are the output of my task.

Now I have a problem, for example, If I need to sort multiple VectorSchemaRoot globally and output it sequentially, my solution is to build a secondary index, sort it, and slice the raw data then output. So I will get a lot of VectorSchemaRoot and a lot of objectId. This puts a lot of pressure on my metadata store. 

I have a preliminary understanding of the principle of using Plasma to store ArrowRecordBatch, I think it's a process of serializing ArrowRecordBatch and deserializing it after reading it. However, the serialization and deserialization utility classes currently provided by Arrow only allow storing or reading a single ArrowRecordBatch.

Here is my sample code

// store a recordBatchList and get a list of objectId
public List<String> storeRecordBatch(Schema schema, List<ArrowRecordBatch> recordBatchList) throws IOException {
List<String> result = new ArrayList<>();
for (ArrowRecordBatch recordBatch : recordBatchList) {
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
WritableByteChannel writableByteChannel = Channels.newChannel(byteArrayOutputStream);
WriteChannel writeChannel = new WriteChannel(writableByteChannel);
MessageSerializer.serialize(writeChannel, schema);
MessageSerializer.serialize(writeChannel, recordBatch);

byte[] id = new byte[20];
do {
new Random().nextBytes(id);
} while (plasmaClient.contains(id));

plasmaClient.put(id, byteArrayOutputStream.toByteArray(), null);
assert plasmaClient.contains(id);
String objectId = ByteBufUtil.hexDump(id);
result.add(objectId);
}
return result;
}

// get a list of ArrowRecordBatch with a list of objectId
public List<ArrowRecordBatch> getRecordBatches(List<String> blockIdList, BufferAllocator allocator) throws IOException {

List<ArrowRecordBatch> recordBatchList = new ArrayList<>();
Schema schema = null;
for (String blockIdStr : blockIdList) {
byte[] blockId = ByteBufUtil.decodeHexDump(blockIdStr);
if (!plasmaClient.contains(blockId)) {
throw new CIMemStoreException(CiMmeStoreResultEnum.BlockNotFoundException);
}
ByteBuffer buffer = plasmaClient.getObjAsByteBuffer(blockId, 0, false);
byte[] bytes = new byte[buffer.capacity()];
buffer.get(bytes);
plasmaClient.release(blockId);
ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(bytes);
ReadableByteChannel readableByteChannel = Channels.newChannel(byteArrayInputStream);
ReadChannel readChannel = new ReadChannel(readableByteChannel);
schema = MessageSerializer.deserializeSchema(readChannel);
ArrowRecordBatch arrowRecordBatch = MessageSerializer.deserializeRecordBatch(readChannel, allocator);
recordBatchList.add(arrowRecordBatch);

}
return recordBatchList;
}

Is there a way to put a list of ArrowRecordBatch to Plasma with one singe id?