/*
 * 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.cassandra.db.index.keys;

import java.nio.ByteBuffer;
import java.util.Set;

import org.apache.cassandra.db.ColumnFamily;
import org.apache.cassandra.db.Column;
import org.apache.cassandra.db.index.AbstractSimplePerColumnSecondaryIndex;
import org.apache.cassandra.db.index.SecondaryIndexSearcher;
import org.apache.cassandra.db.marshal.AbstractType;
import org.apache.cassandra.exceptions.ConfigurationException;

/**
 * Implements a secondary index for a column family using a second column family
 * in which the row keys are indexed values, and column names are base row keys.
 */
public class KeysIndex extends AbstractSimplePerColumnSecondaryIndex
{
    protected ByteBuffer getIndexedValue(ByteBuffer rowKey, Column column)
    {
        return column.value();
    }

    protected ByteBuffer makeIndexColumnName(ByteBuffer rowKey, Column column)
    {
        return rowKey;
    }

    public SecondaryIndexSearcher createSecondaryIndexSearcher(Set<ByteBuffer> columns)
    {
        return new KeysSearcher(baseCfs.indexManager, columns);
    }

    public boolean isIndexEntryStale(ByteBuffer indexedValue, ColumnFamily data, long now)
    {
        Column liveColumn = data.getColumn(columnDef.name);
        if (liveColumn == null || liveColumn.isMarkedForDelete(now))
            return true;

        ByteBuffer liveValue = liveColumn.value();
        return columnDef.getValidator().compare(indexedValue, liveValue) != 0;
    }

    public void validateOptions() throws ConfigurationException
    {
        // no options used
    }

    protected AbstractType getExpressionComparator()
    {
        return baseCfs.getComparator();
    }
}

@@ -1321,22 +1321,93 @@
 mily
+.
 %0A * 
-in which t
+The design uses inverted index http://en.wikipedia.org/wiki/Inverted_index.%0A * T
 he r
@@ -1412,20 +1412,22 @@
  row key
-s ar
+ is th
 e indexe
@@ -1437,45 +1437,209 @@
 alue
-s, and column names are base row keys
+. For example, if we're indexing a column named%0A * city, the index value of city is the row key.%0A * The column names are the keys of the records. To see a detailed example, please%0A * refer to wikipedia
 .%0A *

Improve javadoc for KeysIndex