HDFS-14108. Performance improvement in BlockManager Data Structures. Contributed by Beluga Behr.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java

@@ -34,12 +34,10 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedHashSet;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Queue;
 import java.util.Set;
-import java.util.TreeSet;
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.Callable;
@@ -844,7 +842,7 @@ public class BlockManager implements BlockStatsMXBean {
     // source node returned is not used
     chooseSourceDatanodes(getStoredBlock(block), containingNodes,
         containingLiveReplicasNodes, numReplicas,
-        new LinkedList<Byte>(), LowRedundancyBlocks.LEVEL);
+        new ArrayList<Byte>(), LowRedundancyBlocks.LEVEL);
     
     // containingLiveReplicasNodes can include READ_ONLY_SHARED replicas which are 
     // not included in the numReplicas.liveReplicas() count
@@ -1842,7 +1840,7 @@ public class BlockManager implements BlockStatsMXBean {
   int computeReconstructionWorkForBlocks(
       List<List<BlockInfo>> blocksToReconstruct) {
     int scheduledWork = 0;
-    List<BlockReconstructionWork> reconWork = new LinkedList<>();
+    List<BlockReconstructionWork> reconWork = new ArrayList<>();
 
     // Step 1: categorize at-risk blocks into replication and EC tasks
     namesystem.writeLock();
@@ -1864,14 +1862,10 @@ public class BlockManager implements BlockStatsMXBean {
     }
 
     // Step 2: choose target nodes for each reconstruction task
-    final Set<Node> excludedNodes = new HashSet<>();
-    for(BlockReconstructionWork rw : reconWork){
+    for (BlockReconstructionWork rw : reconWork) {
       // Exclude all of the containing nodes from being targets.
       // This list includes decommissioning or corrupt nodes.
-      excludedNodes.clear();
-      for (DatanodeDescriptor dn : rw.getContainingNodes()) {
-        excludedNodes.add(dn);
-      }
+      final Set<Node> excludedNodes = new HashSet<>(rw.getContainingNodes());
 
       // choose replication targets: NOT HOLDING THE GLOBAL LOCK
       final BlockPlacementPolicy placementPolicy =
@@ -1882,9 +1876,9 @@ public class BlockManager implements BlockStatsMXBean {
     // Step 3: add tasks to the DN
     namesystem.writeLock();
     try {
-      for(BlockReconstructionWork rw : reconWork){
+      for (BlockReconstructionWork rw : reconWork) {
         final DatanodeStorageInfo[] targets = rw.getTargets();
-        if(targets == null || targets.length == 0){
+        if (targets == null || targets.length == 0) {
           rw.resetTargets();
           continue;
         }
@@ -1901,7 +1895,7 @@ public class BlockManager implements BlockStatsMXBean {
 
     if (blockLog.isDebugEnabled()) {
       // log which blocks have been scheduled for reconstruction
-      for(BlockReconstructionWork rw : reconWork){
+      for (BlockReconstructionWork rw : reconWork) {
         DatanodeStorageInfo[] targets = rw.getTargets();
         if (targets != null && targets.length != 0) {
           StringBuilder targetList = new StringBuilder("datanode(s)");
@@ -2666,11 +2660,11 @@ public class BlockManager implements BlockStatsMXBean {
     // Modify the (block-->datanode) map, according to the difference
     // between the old and new block report.
     //
-    Collection<BlockInfoToAdd> toAdd = new LinkedList<>();
-    Collection<BlockInfo> toRemove = new TreeSet<>();
-    Collection<Block> toInvalidate = new LinkedList<>();
-    Collection<BlockToMarkCorrupt> toCorrupt = new LinkedList<>();
-    Collection<StatefulBlockInfo> toUC = new LinkedList<>();
+    Collection<BlockInfoToAdd> toAdd = new ArrayList<>();
+    Collection<BlockInfo> toRemove = new HashSet<>();
+    Collection<Block> toInvalidate = new ArrayList<>();
+    Collection<BlockToMarkCorrupt> toCorrupt = new ArrayList<>();
+    Collection<StatefulBlockInfo> toUC = new ArrayList<>();
 
     boolean sorted = false;
     String strBlockReportId = "";