HBASE-27676 Scan handlers in the RPC executor should match at least one scan queues (#5074)

Signed-off-by: Bryan Beaudreault <bbeaudreault@apache.org>

Author: sunhelly

hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/RWQueueRpcExecutor.java

@@ -79,11 +79,13 @@ public RWQueueRpcExecutor(final String name, final int handlerCount, final int m
     int readQueues = calcNumReaders(this.numCallQueues, callqReadShare);
     int readHandlers = Math.max(readQueues, calcNumReaders(handlerCount, callqReadShare));
 
-    int scanQueues = Math.max(0, (int) Math.floor(readQueues * callqScanShare));
     int scanHandlers = Math.max(0, (int) Math.floor(readHandlers * callqScanShare));
+    int scanQueues =
+      scanHandlers > 0 ? Math.max(1, (int) Math.floor(readQueues * callqScanShare)) : 0;
 
-    if ((readQueues - scanQueues) > 0) {
-      readQueues -= scanQueues;
+    if (scanQueues > 0) {
+      // if scanQueues > 0, the handler count of read should > 0, then we make readQueues >= 1
+      readQueues = Math.max(1, readQueues - scanQueues);
       readHandlers -= scanHandlers;
     } else {
       scanQueues = 0;

hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRpcSchedulerFactory.java

@@ -67,6 +67,18 @@ public void testRWQ() {
     assertTrue(rpcScheduler.getClass().equals(SimpleRpcScheduler.class));
   }
 
+  @Test
+  public void testRWQWithoutReadShare() {
+    // Set some configs just to see how it changes the scheduler. Can't assert the settings had
+    // an effect. Just eyeball the log.
+    this.conf.setDouble(RWQueueRpcExecutor.CALL_QUEUE_READ_SHARE_CONF_KEY, 0);
+    this.conf.setDouble(RpcExecutor.CALL_QUEUE_HANDLER_FACTOR_CONF_KEY, 0.5);
+    this.conf.setDouble(RWQueueRpcExecutor.CALL_QUEUE_SCAN_SHARE_CONF_KEY, 0);
+    RpcSchedulerFactory factory = new SimpleRpcSchedulerFactory();
+    RpcScheduler rpcScheduler = factory.create(this.conf, null, null);
+    assertTrue(rpcScheduler.getClass().equals(SimpleRpcScheduler.class));
+  }
+
   @Test
   public void testFifo() {
     RpcSchedulerFactory factory = new FifoRpcSchedulerFactory();