HBASE-27565 Make the initial corePoolSize configurable for ChoreService (#4958)

Signed-off-by: Duo Zhang <zhangduo@apache.org>

Author: petersomogyi

hbase-common/src/main/java/org/apache/hadoop/hbase/ChoreService.java

@@ -59,6 +59,12 @@ public class ChoreService {
    */
   @InterfaceAudience.Private
   public final static int MIN_CORE_POOL_SIZE = 1;
+  /**
+   * The initial number of threads in the core pool for the {@link ChoreService}.
+   */
+  public static final String CHORE_SERVICE_INITIAL_POOL_SIZE =
+    "hbase.choreservice.initial.pool.size";
+  public static final int DEFAULT_CHORE_SERVICE_INITIAL_POOL_SIZE = 1;
 
   /**
    * This thread pool is used to schedule all of the Chores

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java

@@ -17,6 +17,8 @@
  */
 package org.apache.hadoop.hbase.regionserver;
 
+import static org.apache.hadoop.hbase.ChoreService.CHORE_SERVICE_INITIAL_POOL_SIZE;
+import static org.apache.hadoop.hbase.ChoreService.DEFAULT_CHORE_SERVICE_INITIAL_POOL_SIZE;
 import static org.apache.hadoop.hbase.HConstants.DEFAULT_HBASE_SPLIT_COORDINATED_BY_ZK;
 import static org.apache.hadoop.hbase.HConstants.DEFAULT_HBASE_SPLIT_WAL_MAX_SPLITTER;
 import static org.apache.hadoop.hbase.HConstants.DEFAULT_SLOW_LOG_SYS_TABLE_CHORE_DURATION;
@@ -728,7 +730,9 @@ public HRegionServer(final Configuration conf) throws IOException {
       // and M (An M IS A HRS now). Need to refactor so less duplication between M and its super
       // Master expects Constructor to put up web servers. Ugh.
       // class HRS. TODO.
-      this.choreService = new ChoreService(getName(), true);
+      int choreServiceInitialSize =
+        conf.getInt(CHORE_SERVICE_INITIAL_POOL_SIZE, DEFAULT_CHORE_SERVICE_INITIAL_POOL_SIZE);
+      this.choreService = new ChoreService(getName(), choreServiceInitialSize, true);
       this.executorService = new ExecutorService(getName());
       putUpWebUI();
       span.setStatus(StatusCode.OK);