HDFS-9557. Reduce object allocation in PB conversion. Contributed by Daryn Sharp.

(cherry picked from commit c470c8953d)
(cherry picked from commit e8e3737ce8)

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

@@ -189,7 +189,8 @@ public class PBHelperClient {
   }
 
   public static ByteString getByteString(byte[] bytes) {
-    return ByteString.copyFrom(bytes);
+    // return singleton to reduce object allocation
+    return (bytes.length == 0) ? ByteString.EMPTY : ByteString.copyFrom(bytes);
   }
 
   public static ShmId convert(ShortCircuitShmIdProto shmId) {
@@ -216,8 +217,8 @@ public class PBHelperClient {
 
   public static TokenProto convert(Token<?> tok) {
     return TokenProto.newBuilder().
-        setIdentifier(ByteString.copyFrom(tok.getIdentifier())).
-        setPassword(ByteString.copyFrom(tok.getPassword())).
+        setIdentifier(getByteString(tok.getIdentifier())).
+        setPassword(getByteString(tok.getPassword())).
         setKind(tok.getKind().toString()).
         setService(tok.getService().toString()).build();
   }
@@ -446,16 +447,16 @@ public class PBHelperClient {
         builder.setSuite(convert(option.getCipherSuite()));
       }
       if (option.getInKey() != null) {
-        builder.setInKey(ByteString.copyFrom(option.getInKey()));
+        builder.setInKey(getByteString(option.getInKey()));
       }
       if (option.getInIv() != null) {
-        builder.setInIv(ByteString.copyFrom(option.getInIv()));
+        builder.setInIv(getByteString(option.getInIv()));
       }
       if (option.getOutKey() != null) {
-        builder.setOutKey(ByteString.copyFrom(option.getOutKey()));
+        builder.setOutKey(getByteString(option.getOutKey()));
       }
       if (option.getOutIv() != null) {
-        builder.setOutIv(ByteString.copyFrom(option.getOutIv()));
+        builder.setOutIv(getByteString(option.getOutIv()));
       }
       return builder.build();
     }
@@ -1676,8 +1677,8 @@ public class PBHelperClient {
     DataEncryptionKeyProto.Builder b = DataEncryptionKeyProto.newBuilder()
         .setKeyId(bet.keyId)
         .setBlockPoolId(bet.blockPoolId)
-        .setNonce(ByteString.copyFrom(bet.nonce))
-        .setEncryptionKey(ByteString.copyFrom(bet.encryptionKey))
+        .setNonce(getByteString(bet.nonce))
+        .setEncryptionKey(getByteString(bet.encryptionKey))
         .setExpiryDate(bet.expiryDate);
     if (bet.encryptionAlgorithm != null) {
       b.setEncryptionAlgorithm(bet.encryptionAlgorithm);
@@ -1754,10 +1755,10 @@ public class PBHelperClient {
             setGroup(fs.getGroup()).
             setFileId(fs.getFileId()).
             setChildrenNum(fs.getChildrenNum()).
-            setPath(ByteString.copyFrom(fs.getLocalNameInBytes())).
+            setPath(getByteString(fs.getLocalNameInBytes())).
             setStoragePolicy(fs.getStoragePolicy());
     if (fs.isSymlink())  {
-      builder.setSymlink(ByteString.copyFrom(fs.getSymlinkInBytes()));
+      builder.setSymlink(getByteString(fs.getSymlinkInBytes()));
     }
     if (fs.getFileEncryptionInfo() != null) {
       builder.setFileEncryptionInfo(convert(fs.getFileEncryptionInfo()));
@@ -1780,7 +1781,7 @@ public class PBHelperClient {
     int snapshotNumber = status.getSnapshotNumber();
     int snapshotQuota = status.getSnapshotQuota();
     byte[] parentFullPath = status.getParentFullPath();
-    ByteString parentFullPathBytes = ByteString.copyFrom(
+    ByteString parentFullPathBytes = getByteString(
         parentFullPath == null ? DFSUtilClient.EMPTY_BYTES : parentFullPath);
     HdfsFileStatusProto fs = convert(status.getDirStatus());
     SnapshottableDirectoryStatusProto.Builder builder =
@@ -1995,7 +1996,7 @@ public class PBHelperClient {
     if (entry == null) {
       return null;
     }
-    ByteString sourcePath = ByteString.copyFrom(entry.getSourcePath() == null ?
+    ByteString sourcePath = getByteString(entry.getSourcePath() == null ?
         DFSUtilClient.EMPTY_BYTES : entry.getSourcePath());
     String modification = entry.getType().getLabel();
     SnapshotDiffReportEntryProto.Builder builder = SnapshotDiffReportEntryProto
@@ -2003,7 +2004,7 @@ public class PBHelperClient {
         .setModificationLabel(modification);
     if (entry.getType() == DiffType.RENAME) {
       ByteString targetPath =
-          ByteString.copyFrom(entry.getTargetPath() == null ?
+          getByteString(entry.getTargetPath() == null ?
               DFSUtilClient.EMPTY_BYTES : entry.getTargetPath());
       builder.setTargetPath(targetPath);
     }

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -859,6 +859,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-8894. Set SO_KEEPALIVE on DN server sockets.
     (Kanaka Kumar Avvaru via wang)
 
+    HDFS-9557. Reduce object allocation in PB conversion
+    (Daryn Sharp via cnauroth)
+
   OPTIMIZATIONS
 
     HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/PBHelper.java

@@ -209,7 +209,7 @@ public class PBHelper {
 
   public static BlockKeyProto convert(BlockKey key) {
     byte[] encodedKey = key.getEncodedKey();
-    ByteString keyBytes = ByteString.copyFrom(encodedKey == null ?
+    ByteString keyBytes = PBHelperClient.getByteString(encodedKey == null ?
         DFSUtilClient.EMPTY_BYTES : encodedKey);
     return BlockKeyProto.newBuilder().setKeyId(key.getKeyId())
         .setKeyBytes(keyBytes).setExpiryDate(key.getExpiryDate()).build();

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/protocolPB/TestPBHelper.java

@@ -19,6 +19,7 @@ package org.apache.hadoop.hdfs.protocolPB;
 
 import static org.hamcrest.CoreMatchers.is;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
 
@@ -89,6 +90,7 @@ import org.junit.Test;
 import com.google.common.base.Joiner;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
+import com.google.protobuf.ByteString;
 
 /**
  * Tests for {@link PBHelper}
@@ -100,6 +102,11 @@ public class TestPBHelper {
    */
   private static final double DELTA = 0.000001;
 
+  @Test
+  public void testGetByteString() {
+    assertSame(ByteString.EMPTY, PBHelperClient.getByteString(new byte[0]));
+  }
+
   @Test
   public void testConvertNamenodeRole() {
     assertEquals(NamenodeRoleProto.BACKUP,