szetszwo commented on code in PR #6613:
URL: https://github.com/apache/ozone/pull/6613#discussion_r2461180608
##########
hadoop-hdds/client/src/main/java/org/apache/hadoop/hdds/scm/XceiverClientGrpc.java:
##########
@@ -504,6 +516,65 @@ private XceiverClientReply sendCommandWithRetry(
}
}
+ /**
+ * Starts a streaming read operation, intended to read entire blocks from
the datanodes. This method expects a
+ * {@link StreamObserver} to be passed in, which will be used to receive the
streamed data from the datanode.
+ * Upon successfully starting the streaming read, a {@link
StreamingReadResponse} is returned, which contains
+ * information about the datanode used for the read, and the request
observer that can be used to manage the stream
+ * (e.g., to cancel it if needed). A semaphore is acquired to limit the
number of concurrent streaming reads so upon
+ * successful return of this method, the caller must ensure to call {@link
#completeStreamRead(StreamingReadResponse)}
+ * to release the semaphore once the streaming read is complete.
+ * @param request The container command request to initiate the streaming
read.
+ * @param streamObserver The observer that will handle the streamed
responses.
+ * @return A {@link StreamingReadResponse} containing details of the
streaming read operation.
+ * @throws IOException
+ * @throws InterruptedException
+ */
+ @Override
+ public StreamingReadResponse streamRead(ContainerCommandRequestProto request,
+ StreamObserver<ContainerCommandResponseProto> streamObserver) throws
IOException, InterruptedException {
+ List<DatanodeDetails> datanodeList = sortDatanodes(request);
+ IOException lastException = null;
+ for (DatanodeDetails dn : datanodeList) {
+ try {
+ checkOpen(dn);
+ semaphore.acquire();
+ XceiverClientProtocolServiceStub stub = asyncStubs.get(dn.getID());
+ if (stub == null) {
+ throw new IOException("Failed to get gRPC stub for DataNode: " + dn);
+ }
+ if (LOG.isDebugEnabled()) {
+ LOG.debug("Executing command {} on datanode {}",
processForDebug(request), dn);
+ }
+ StreamObserver<ContainerCommandRequestProto> requestObserver = stub
+ .withDeadlineAfter(timeout, TimeUnit.SECONDS)
+ .send(streamObserver);
+ requestObserver.onNext(request);
+ requestObserver.onCompleted();
+ return new StreamingReadResponse(dn,
(ClientCallStreamObserver<ContainerCommandRequestProto>) requestObserver);
Review Comment:
> However its still not clear to me if I need to call onComplete() ...
It should not be. If we call `onComplete()` right after `onNext()`, a gRPC
stream can only send one request with a fixed length. Then, a stream won't be
able to support multiple read below or it has to read the entire blocks all the
time.
Suppose A block has 128 MB.
- Case 1
1. A client application opens the file.
2. It calls read() with 10KB initially
3. It calls read() with 50MB more.
4. ... // the client could call read() any number of times with an
arbitrary length.
- Case 2
1. A client application opens the file.
2. It calls read() with 10KB.
3. It leaves the file open for 1 minute.
4. It closes the file.
If we only have one request per stream, how to set the data length for both
cases? If we read the entire block all the time, Case 2 is inefficient.
Otherwise, we don't read the entire block. Then, it have to open multiple gRPC
streams for case 1.
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