HBASE-1481 Add fast row key only scanning

git-svn-id: https://svn.apache.org/repos/asf/hadoop/hbase/trunk@822062 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -97,6 +97,7 @@ Release 0.21.0 - Unreleased
    HBASE-1879  ReadOnly transactions generate WAL activity (Clint Morgan via Stack)
    HBASE-1875  Compression test utility
    HBASE-1832  Faster enable/disable/delete
+   HBASE-1481  Add fast row key only scanning
 
   OPTIMIZATIONS
 

bin/HBase.rb

@@ -18,6 +18,7 @@ import org.apache.hadoop.hbase.client.Get
 import org.apache.hadoop.hbase.client.Put
 import org.apache.hadoop.hbase.client.Scan
 import org.apache.hadoop.hbase.client.Delete
+import org.apache.hadoop.hbase.filter.FirstKeyOnlyFilter
 import org.apache.hadoop.hbase.HConstants
 import org.apache.hadoop.hbase.io.hfile.Compression
 import org.apache.hadoop.hbase.HBaseConfiguration
@@ -544,6 +545,7 @@ module HBase
       now = Time.now
       scan = Scan.new()
       scan.setCacheBlocks(false)
+      scan.setFilter(FirstKeyOnlyFilter.new())
       s = @table.getScanner(scan)
       count = 0
       i = s.iterator()

src/java/org/apache/hadoop/hbase/filter/FirstKeyOnlyFilter.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2009 The Apache Software Foundation
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hbase.filter;
+
+import org.apache.hadoop.hbase.KeyValue;
+
+import java.io.DataOutput;
+import java.io.IOException;
+import java.io.DataInput;
+
+/**
+ * A filter that will only return the first KV from each row.
+ * <p>
+ * This filter can be used to more efficiently perform row count operations.
+ */
+public class FirstKeyOnlyFilter implements Filter {
+  private boolean foundKV = false;
+
+  public FirstKeyOnlyFilter() {
+  }
+
+  public void reset() {
+    foundKV = false;
+  }
+
+  public boolean filterRowKey(byte[] buffer, int offset, int length) {
+    return false;
+  }
+
+  public boolean filterAllRemaining() {
+    return false;
+  }
+
+  public ReturnCode filterKeyValue(KeyValue v) {
+    if(foundKV) return ReturnCode.NEXT_ROW;
+    foundKV = true;
+    return ReturnCode.INCLUDE;
+  }
+
+  public boolean filterRow() {
+    return false;
+  }
+
+  public void write(DataOutput out) throws IOException {
+  }
+
+  public void readFields(DataInput in) throws IOException {
+  }
+}

src/java/org/apache/hadoop/hbase/io/HbaseObjectWritable.java

@@ -149,6 +149,7 @@ public class HbaseObjectWritable implements Writable, Configurable {
     addToMap(QualifierFilter.class, code++);
     addToMap(SkipFilter.class, code++);
     addToMap(WritableByteArrayComparable.class, code++);
+    addToMap(FirstKeyOnlyFilter.class, code++);
 
     addToMap(Delete [].class, code++);
   }

src/java/org/apache/hadoop/hbase/mapreduce/RowCounter.java

@@ -26,6 +26,7 @@ import org.apache.hadoop.hbase.HBaseConfiguration;
 import org.apache.hadoop.hbase.KeyValue;
 import org.apache.hadoop.hbase.client.Result;
 import org.apache.hadoop.hbase.client.Scan;
+import org.apache.hadoop.hbase.filter.FirstKeyOnlyFilter;
 import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
 import org.apache.hadoop.hbase.util.Bytes;
 import org.apache.hadoop.mapreduce.Job;
@@ -96,6 +97,7 @@ public class RowCounter {
       sb.append(args[i]);
     }
     Scan scan = new Scan();
+    scan.setFilter(new FirstKeyOnlyFilter());
     if (sb.length() > 0) {
       for (String columnName :sb.toString().split(" ")) {
         String [] fields = columnName.split(":");

src/test/org/apache/hadoop/hbase/filter/TestFilter.java

@@ -789,6 +789,21 @@ public class TestFilter extends HBaseTestCase {
     
   }
   
+  public void testFirstKeyOnlyFilter() throws IOException {
+    Scan s = new Scan();
+    s.setFilter(new FirstKeyOnlyFilter());
+    // Expected KVs, the first KV from each of the remaining 6 rows
+    KeyValue [] kvs = {
+        new KeyValue(ROWS_ONE[0], FAMILIES[0], QUALIFIERS_ONE[0], VALUES[0]),
+        new KeyValue(ROWS_ONE[2], FAMILIES[0], QUALIFIERS_ONE[0], VALUES[0]),
+        new KeyValue(ROWS_ONE[3], FAMILIES[0], QUALIFIERS_ONE[0], VALUES[0]),
+        new KeyValue(ROWS_TWO[0], FAMILIES[0], QUALIFIERS_TWO[0], VALUES[1]),
+        new KeyValue(ROWS_TWO[2], FAMILIES[0], QUALIFIERS_TWO[0], VALUES[1]),
+        new KeyValue(ROWS_TWO[3], FAMILIES[0], QUALIFIERS_TWO[0], VALUES[1])
+    };
+    verifyScanFull(s, kvs);
+  }
+  
   public void testSingleColumnValueFilter() throws IOException {
     
     // From HBASE-1821