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Main 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 org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode;

/**
 * Implementing classes of this interface will be used for the tracking
 * and enforcement of columns and numbers of versions and timeToLive during
 * the course of a Get or Scan operation.
 * 
 * Currently there are two different types of Store/Family-level queries.
 * 
{@link ExplicitColumnTracker} is used when the query specifies
 * one or more column qualifiers to return in the family.
 * {@link ScanWildcardColumnTracker} is used when no columns are
 * explicitly specified.
 * 
 * 
 * This class is utilized by {@link ScanQueryMatcher} mainly through two methods:
 * 
{@link #checkColumn} is called when a Put satisfies all other
 * conditions of the query.
 * {@link #getNextRowOrNextColumn} is called whenever ScanQueryMatcher
 * believes that the current column should be skipped (by timestamp, filter etc.)
 * 
 * 
 * These two methods returns a 
 * {@link org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode}
 * to define what action should be taken.
 * 
 * This class is NOT thread-safe as queries are never multi-threaded
 */
@InterfaceAudience.Private
public interface ColumnTracker {

  /**
   * Checks if the column is present in the list of requested columns by returning the match code
   * instance. It does not check against the number of versions for the columns asked for. To do the
   * version check, one has to call {@link #checkVersions(byte[], int, int, long, byte, boolean)}
   * method based on the return type (INCLUDE) of this method. The values that can be returned by
   * this method are {@link MatchCode#INCLUDE}, {@link MatchCode#SEEK_NEXT_COL} and
   * {@link MatchCode#SEEK_NEXT_ROW}.
   * @param bytes
   * @param offset
   * @param length
   * @param type The type of the KeyValue
   * @return The match code instance.
   * @throws IOException in case there is an internal consistency problem caused by a data
   *           corruption.
   */
  ScanQueryMatcher.MatchCode checkColumn(byte[] bytes, int offset, int length, byte type)
      throws IOException;

  /**
   * Keeps track of the number of versions for the columns asked for. It assumes that the user has
   * already checked if the keyvalue needs to be included by calling the
   * {@link #checkColumn(byte[], int, int, byte)} method. The enum values returned by this method
   * are {@link MatchCode#SKIP}, {@link MatchCode#INCLUDE},
   * {@link MatchCode#INCLUDE_AND_SEEK_NEXT_COL} and {@link MatchCode#INCLUDE_AND_SEEK_NEXT_ROW}.
   * Implementations which include all the columns could just return {@link MatchCode#INCLUDE} in
   * the {@link #checkColumn(byte[], int, int, byte)} method and perform all the operations in this
   * checkVersions method.
   * @param type the type of the key value (Put/Delete)
   * @param ttl The timeToLive to enforce.
   * @param ignoreCount indicates if the KV needs to be excluded while counting (used during
   *          compactions. We only count KV's that are older than all the scanners' read points.)
   * @return the scan query matcher match code instance
   * @throws IOException in case there is an internal consistency problem caused by a data
   *           corruption.
   */
  ScanQueryMatcher.MatchCode checkVersions(byte[] bytes, int offset, int length, long ttl,
      byte type, boolean ignoreCount) throws IOException;
  /**
   * Resets the Matcher
   */
  void reset();

  /**
   *
   * @return true when done.
   */
  boolean done();

  /**
   * Used by matcher and scan/get to get a hint of the next column
   * to seek to after checkColumn() returns SKIP.  Returns the next interesting
   * column we want, or NULL there is none (wildcard scanner).
   *
   * Implementations aren't required to return anything useful unless the most recent
   * call was to checkColumn() and the return code was SKIP.  This is pretty implementation
   * detail-y, but optimizations are like that.
   *
   * @return null, or a ColumnCount that we should seek to
   */
  ColumnCount getColumnHint();

  /**
   * Retrieve the MatchCode for the next row or column
   */
  MatchCode getNextRowOrNextColumn(
    byte[] bytes, int offset, int qualLength
  );

  /**
   * Give the tracker a chance to declare it's done based on only the timestamp
   * to allow an early out.
   *
   * @param timestamp
   * @return true to early out based on timestamp.
   */
  boolean isDone(long timestamp);
}