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Server functionality for HBase
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/**
 *
 * 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.regionserver;

import java.io.IOException;
import java.util.List;

import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.classification.InterfaceStability;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.HBaseInterfaceAudience;
import org.apache.hadoop.hbase.HRegionInfo;

/**
 * RegionScanner describes iterators over rows in an HRegion.
 */
@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
@InterfaceStability.Stable
public interface RegionScanner extends InternalScanner {
  /**
   * @return The RegionInfo for this scanner.
   */
  HRegionInfo getRegionInfo();

  /**
   * @return True if a filter indicates that this scanner will return no further rows.
   * @throws IOException in case of I/O failure on a filter.
   */
  boolean isFilterDone() throws IOException;

  /**
   * Do a reseek to the required row. Should not be used to seek to a key which
   * may come before the current position. Always seeks to the beginning of a
   * row boundary.
   *
   * @throws IOException
   * @throws IllegalArgumentException
   *           if row is null
   *
   */
  boolean reseek(byte[] row) throws IOException;

  /**
   * @return The preferred max buffersize. See 
   * {@link org.apache.hadoop.hbase.client.Scan#setMaxResultSize(long)}
   */
  long getMaxResultSize();

  /**
   * @return The Scanner's MVCC readPt see {@link MultiVersionConsistencyControl}
   */
  long getMvccReadPoint();

  /**
   * Grab the next row's worth of values with the default limit on the number of values
   * to return.
   * This is a special internal method to be called from coprocessor hooks to avoid expensive setup.
   * Caller must set the thread's readpoint, start and close a region operation, an 
   * synchronize on the scanner object. Caller should maintain and update metrics.
   * See {@link #nextRaw(List, int)}
   * @param result return output array
   * @return true if more rows exist after this one, false if scanner is done
   * @throws IOException e
   */
  boolean nextRaw(List result) throws IOException;

  /**
   * Grab the next row's worth of values with a limit on the number of values
   * to return.
   * This is a special internal method to be called from coprocessor hooks to avoid expensive setup.
   * Caller must set the thread's readpoint, start and close a region operation, an synchronize on the scanner object.
   * Example:
   *    * HRegion region = ...;
   * RegionScanner scanner = ...
   * MultiVersionConsistencyControl.setThreadReadPoint(scanner.getMvccReadPoint());
   * region.startRegionOperation();
   * try {
   *   synchronized(scanner) {
   *     ...
   *     boolean moreRows = scanner.nextRaw(values);
   *     ...
   *   }
   * } finally {
   *   region.closeRegionOperation();
   * }
   * 
   * @param result return output array
   * @param limit limit on row count to get
   * @return true if more rows exist after this one, false if scanner is done
   * @throws IOException e
   */
  boolean nextRaw(List result, int limit) throws IOException;
}