hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RegionScanner.java

/**
 *
 * 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.Cell;
import org.apache.hadoop.hbase.HBaseInterfaceAudience;
import org.apache.hadoop.hbase.client.RegionInfo;
import org.apache.yetus.audience.InterfaceAudience;
import org.apache.yetus.audience.InterfaceStability;

/**
 * RegionScanner describes iterators over rows in an HRegion.
 */
@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
@InterfaceStability.Evolving
public interface RegionScanner extends InternalScanner {
  /**
   * @return The RegionInfo for this scanner.
   */
  RegionInfo 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 MultiVersionConcurrencyControl}
   */
  long getMvccReadPoint();

  /**
   * @return The limit on the number of cells to retrieve on each call to next(). See
   *         {@link org.apache.hadoop.hbase.client.Scan#setBatch(int)}
   */
  int getBatch();

  /**
   * Grab the next row's worth of values. 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, ScannerContext)}
   * @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<Cell> result) throws IOException;

  /**
   * Grab the next row's worth of values. The {@link ScannerContext} is used to enforce and track
   * any limits associated with this call. Any progress that exists in the {@link ScannerContext}
   * prior to calling this method will be LOST if {@link ScannerContext#getKeepProgress()} is false.
   * Upon returning from this method, the {@link ScannerContext} will contain information about the
   * progress made towards the limits. 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: <code>
   * HRegion region = ...;
   * RegionScanner scanner = ...
   * MultiVersionConcurrencyControl.setThreadReadPoint(scanner.getMvccReadPoint());
   * region.startRegionOperation();
   * try {
   *   synchronized(scanner) {
   *     ...
   *     boolean moreRows = scanner.nextRaw(values);
   *     ...
   *   }
   * } finally {
   *   region.closeRegionOperation();
   * }
   * </code>
   * @param result return output array
   * @param scannerContext The {@link ScannerContext} instance encapsulating all limits that should
   *          be tracked during calls to this method. The progress towards these limits can be
   *          tracked within this instance.
   * @return true if more rows exist after this one, false if scanner is done
   * @throws IOException e
   */
  boolean nextRaw(List<Cell> result, ScannerContext scannerContext)
      throws IOException;
}