HDFS-14535. The default 8KB buffer in requestFileDescriptors#BufferedOutputStream is causing lots of heap allocation in HBase when using short-circut read

Author: openinx

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/client/impl/BlockReaderFactory.java

@@ -86,6 +86,7 @@
 @InterfaceAudience.Private
 public class BlockReaderFactory implements ShortCircuitReplicaCreator {
   static final Logger LOG = LoggerFactory.getLogger(BlockReaderFactory.class);
+  private static final int SMALL_BUFFER_SIZE = 512;
 
   public static class FailureInjector {
     public void injectRequestFileDescriptorsFailure() throws IOException {
@@ -582,7 +583,7 @@ private ShortCircuitReplicaInfo requestFileDescriptors(DomainPeer peer,
           Slot slot) throws IOException {
     ShortCircuitCache cache = clientContext.getShortCircuitCache();
     final DataOutputStream out =
-        new DataOutputStream(new BufferedOutputStream(peer.getOutputStream()));
+        new DataOutputStream(new BufferedOutputStream(peer.getOutputStream(), SMALL_BUFFER_SIZE));
     SlotId slotId = slot == null ? null : slot.getSlotId();
     new Sender(out).requestShortCircuitFds(block, token, slotId, 1,
         failureInjector.getSupportsReceiptVerification());