HBASE-13333 Renew Scanner Lease without advancing the RegionScanner.

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AbstractClientScanner.java

@@ -124,4 +124,11 @@ public abstract class AbstractClientScanner implements ResultScanner {
       }
     };
   }
+  /**
+   * Allow the client to renew the scanner's lease on the server.
+   * @return true if the lease was successfully renewed, false otherwise.
+   */
+  // Note that this method should be on ResultScanner, but that is marked stable.
+  // Callers have to cast their instance of ResultScanner to AbstractClientScanner to use this.
+  public abstract boolean renewLease();
 }

hbase-client/src/main/java/org/apache/hadoop/hbase/client/ClientScanner.java

@@ -752,4 +752,21 @@ public class ClientScanner extends AbstractClientScanner {
       return closestFrontRow;
     }
   }
+
+  @Override
+  public boolean renewLease() {
+    if (callable != null) {
+      // do not return any rows, do not advance the scanner
+      callable.setCaching(0);
+      try {
+        this.caller.callWithoutRetries(callable, this.scannerTimeout);
+      } catch (Exception e) {
+        return false;
+      } finally {
+        callable.setCaching(this.caching);
+      }
+      return true;
+    }
+    return false;
+  }
 }

hbase-server/src/main/java/org/apache/hadoop/hbase/client/ClientSideRegionScanner.java

@@ -109,4 +109,9 @@ public class ClientSideRegionScanner extends AbstractClientScanner {
       }
     }
   }
+
+  @Override
+  public boolean renewLease() {
+    throw new UnsupportedOperationException();
+  }
 }

hbase-server/src/main/java/org/apache/hadoop/hbase/client/TableSnapshotScanner.java

@@ -201,4 +201,9 @@ public class TableSnapshotScanner extends AbstractClientScanner {
     }
   }
 
+  @Override
+  public boolean renewLease() {
+    throw new UnsupportedOperationException();
+  }
+
 }

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestFromClientSide3.java

@@ -22,6 +22,7 @@ package org.apache.hadoop.hbase.client;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.fail;
 
 import java.util.ArrayList;
@@ -428,4 +429,29 @@ public class TestFromClientSide3 {
     assertTrue(Arrays.equals(res.getValue(FAMILY, COL_QUAL), VAL_BYTES));
     table.close();
   }
+
+  @Test
+  public void testLeaseRenewal() throws Exception {
+    HTable table = TEST_UTIL.createTable(
+      Bytes.toBytes("testLeaseRenewal"), FAMILY);
+    Put p = new Put(ROW_BYTES);
+    p.add(FAMILY, COL_QUAL, VAL_BYTES);
+    table.put(p);
+    p = new Put(ANOTHERROW);
+    p.add(FAMILY, COL_QUAL, VAL_BYTES);
+    table.put(p);
+    Scan s = new Scan();
+    s.setCaching(1);
+    ResultScanner rs = table.getScanner(s);
+    // make sure that calling renewLease does not impact the scan results
+    assertTrue(((AbstractClientScanner)rs).renewLease());
+    assertTrue(Arrays.equals(rs.next().getRow(), ANOTHERROW));
+    assertTrue(((AbstractClientScanner)rs).renewLease());
+    assertTrue(Arrays.equals(rs.next().getRow(), ROW_BYTES));
+    assertTrue(((AbstractClientScanner)rs).renewLease());
+    assertNull(rs.next());
+    assertFalse(((AbstractClientScanner)rs).renewLease());
+    rs.close();
+    table.close();
+  }
 }