HDFS-12412. Change ErasureCodingWorker.stripedReadPool to cached thread pool. (Lei (Eddy) Xu)

(cherry picked from commit 123342cd0759ff88801d4f5ab10987f6e3f344b0)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -569,8 +569,6 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
       "dfs.namenode.ec.system.default.policy";
   public static final String  DFS_NAMENODE_EC_SYSTEM_DEFAULT_POLICY_DEFAULT =
       "RS-6-3-1024k";
-  public static final String  DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_THREADS_KEY = "dfs.datanode.ec.reconstruction.stripedread.threads";
-  public static final int     DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_THREADS_DEFAULT = 20;
   public static final String  DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_BUFFER_SIZE_KEY = "dfs.datanode.ec.reconstruction.stripedread.buffer.size";
   public static final int     DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_BUFFER_SIZE_DEFAULT = 64 * 1024;
   public static final String  DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_TIMEOUT_MILLIS_KEY = "dfs.datanode.ec.reconstruction.stripedread.timeout.millis";

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

@@ -55,19 +55,19 @@ public final class ErasureCodingWorker {
     this.datanode = datanode;
     this.conf = conf;
 
-    initializeStripedReadThreadPool(conf.getInt(
-        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_THREADS_KEY,
-        DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_STRIPED_READ_THREADS_DEFAULT));
+    initializeStripedReadThreadPool();
     initializeStripedBlkReconstructionThreadPool(conf.getInt(
         DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_THREADS_KEY,
         DFSConfigKeys.DFS_DN_EC_RECONSTRUCTION_THREADS_DEFAULT));
   }
 
-  private void initializeStripedReadThreadPool(int num) {
-    LOG.debug("Using striped reads; pool threads={}", num);
+  private void initializeStripedReadThreadPool() {
+    LOG.debug("Using striped reads");
 
-    stripedReadPool = new ThreadPoolExecutor(1, num, 60, TimeUnit.SECONDS,
-        new SynchronousQueue<Runnable>(),
+    // Essentially, this is a cachedThreadPool.
+    stripedReadPool = new ThreadPoolExecutor(0, Integer.MAX_VALUE,
+        60, TimeUnit.SECONDS,
+        new SynchronousQueue<>(),
         new Daemon.DaemonFactory() {
           private final AtomicInteger threadIndex = new AtomicInteger(0);
 

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

@@ -3056,15 +3056,6 @@
   </description>
 </property>
 
-<property>
-  <name>dfs.datanode.ec.reconstruction.stripedread.threads</name>
-  <value>20</value>
-  <description>
-    Number of threads used by the Datanode to read striped block
-    during background reconstruction work.
-  </description>
-</property>
-
 <property>
   <name>dfs.datanode.ec.reconstruction.stripedread.buffer.size</name>
   <value>65536</value>

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSErasureCoding.md

@@ -134,7 +134,6 @@ Deployment
   Erasure coding background recovery work on the DataNodes can also be tuned via the following configuration parameters:
 
   1. `dfs.datanode.ec.reconstruction.stripedread.timeout.millis` - Timeout for striped reads. Default value is 5000 ms.
-  1. `dfs.datanode.ec.reconstruction.stripedread.threads` - Number of concurrent reader threads. Default value is 20 threads.
   1. `dfs.datanode.ec.reconstruction.stripedread.buffer.size` - Buffer size for reader service. Default value is 64KB.
   1. `dfs.datanode.ec.reconstruction.threads` - Number of threads used by the Datanode for background reconstruction work. Default value is 8 threads.