HDFS-14844. Make buffer of BlockReaderRemote#newBlockReader#BufferedOutputStream configurable. Contributed by Lisheng Sun.

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

@@ -148,6 +148,9 @@ public interface HdfsClientConfigKeys {
           "dfs.client.key.provider.cache.expiry";
   long    DFS_CLIENT_KEY_PROVIDER_CACHE_EXPIRY_DEFAULT =
               TimeUnit.DAYS.toMillis(10); // 10 days
+  String DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_KEY =
+      "dfs.client.block.reader.remote.buffer.size";
+  int DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_DEFAULT = 8192;
 
   String  DFS_DATANODE_KERBEROS_PRINCIPAL_KEY =
       "dfs.datanode.kerberos.principal";

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

@@ -855,7 +855,7 @@ public class BlockReaderFactory implements ShortCircuitReplicaCreator {
         fileName, block, token, startOffset, length,
         verifyChecksum, clientName, peer, datanode,
         clientContext.getPeerCache(), cachingStrategy,
-        networkDistance);
+        networkDistance, configuration);
   }
 
   @Override

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

@@ -29,6 +29,7 @@ import java.util.EnumSet;
 import java.util.UUID;
 
 import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.ReadOption;
 import org.apache.hadoop.hdfs.BlockReader;
 import org.apache.hadoop.hdfs.PeerCache;
@@ -55,6 +56,9 @@ import com.google.common.annotations.VisibleForTesting;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_DEFAULT;
+import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_KEY;
+
 /**
  * This is a wrapper around connection to datanode
  * and understands checksum, offset etc.
@@ -391,10 +395,13 @@ public class BlockReaderRemote implements BlockReader {
       Peer peer, DatanodeID datanodeID,
       PeerCache peerCache,
       CachingStrategy cachingStrategy,
-      int networkDistance) throws IOException {
+      int networkDistance, Configuration configuration) throws IOException {
     // in and out will be closed when sock is closed (by the caller)
+    int bufferSize = configuration.getInt(
+        DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_KEY,
+        DFS_CLIENT_BLOCK_READER_REMOTE_BUFFER_SIZE_DEFAULT);
     final DataOutputStream out = new DataOutputStream(new BufferedOutputStream(
-        peer.getOutputStream()));
+        peer.getOutputStream(), bufferSize));
     new Sender(out).readBlock(block, blockToken, clientName, startOffset, len,
         verifyChecksum, cachingStrategy);
 

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/StripedBlockReader.java

@@ -129,7 +129,7 @@ class StripedBlockReader {
       return BlockReaderRemote.newBlockReader(
           "dummy", block, blockToken, offsetInBlock,
           block.getNumBytes() - offsetInBlock, true, "", peer, source,
-          null, stripedReader.getCachingStrategy(), -1);
+          null, stripedReader.getCachingStrategy(), -1, conf);
     } catch (IOException e) {
       LOG.info("Exception while creating remote block reader, datanode {}",
           source, e);

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -4098,6 +4098,18 @@
   </description>
 </property>
 
+  <property>
+    <name>dfs.client.block.reader.remote.buffer.size</name>
+    <value>8192</value>
+    <description>
+      The output stream buffer size of a DFSClient remote read. The buffer default value is 8KB. The buffer includes
+      only some request parameters that are: block, blockToken, clientName, startOffset, len, verifyChecksum,
+      cachingStrategy.
+      It is recommended to adjust the value according to the workload, which can reduce unnecessary memory
+      usage and the frequency of the garbage collection. A value of 512 might be reasonable.
+    </description>
+  </property>
+
 <property>
   <name>dfs.content-summary.limit</name>
   <value>5000</value>