Revert "HBASE-22715 All scan requests should be handled by scan handl…

…er threads in RWQueueRpcExecutor (#393)"

This reverts commit 55bd5ec.

Incorrect application to branch-1.3. HBASE-22715 is relevant only where HBASE-17508
was committed.

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

@@ -234,7 +234,12 @@ private boolean isWriteRequest(final RequestHeader header, final Message param)
   }
 
   private boolean isScanRequest(final RequestHeader header, final Message param) {
-    return param instanceof ScanRequest;
+    if (param instanceof ScanRequest) {
+      // The first scan request will be executed as a "short read"
+      ScanRequest request = (ScanRequest)param;
+      return request.hasScannerId();
+    }
+    return false;
   }
 
   @Override

hbase-server/src/test/java/org/apache/hadoop/hbase/ipc/TestSimpleRpcScheduler.java

@@ -292,7 +292,7 @@ public void testScanQueues() throws Exception {
 
       CallRunner scanCallTask = mock(CallRunner.class);
       RpcServer.Call scanCall = mock(RpcServer.Call.class);
-      scanCall.param = ScanRequest.newBuilder().build();
+      scanCall.param = ScanRequest.newBuilder().setScannerId(1).build();
       RequestHeader scanHead = RequestHeader.newBuilder().setMethodName("scan").build();
       when(scanCallTask.getCall()).thenReturn(scanCall);
       when(scanCall.getHeader()).thenReturn(scanHead);