Filter

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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.filter;

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.KeyValue;
import org.apache.hadoop.hbase.exceptions.DeserializationException;

/**
 * Interface for row and column filters directly applied within the regionserver.
 *
 * A filter can expect the following call sequence:
 * <ul>
 *   <li> {@link #reset()} : reset the filter state before filtering a new row. </li>
 *   <li> {@link #filterAllRemaining()}: true means row scan is over; false means keep going. </li>
 *   <li> {@link #filterRowKey(byte[],int,int)}: true means drop this row; false means include.</li>
 *   <li> {@link #filterKeyValue(Cell)}: decides whether to include or exclude this KeyValue.
 *        See {@link ReturnCode}. </li>
 *   <li> {@link #transform(KeyValue)}: if the KeyValue is included, let the filter transform the
 *        KeyValue. </li>
 *   <li> {@link #filterRowCells(List)}: allows direct modification of the final list to be submitted
 *   <li> {@link #filterRow()}: last chance to drop entire row based on the sequence of
 *        filter calls. Eg: filter a row if it doesn't contain a specified column. </li>
 * </ul>
 *
 * Filter instances are created one per region/scan.  This abstract class replaces
 * the old RowFilterInterface.
 *
 * When implementing your own filters, consider inheriting {@link FilterBase} to help
 * you reduce boilerplate.
 *
 * @see FilterBase
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class Filter {
  protected transient boolean reversed;
  /**
   * Reset the state of the filter between rows.
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract public void reset() throws IOException;

  /**
   * Filters a row based on the row key. If this returns true, the entire row will be excluded. If
   * false, each KeyValue in the row will be passed to {@link #filterKeyValue(Cell)} below.
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @param buffer buffer containing row key
   * @param offset offset into buffer where row key starts
   * @param length length of the row key
   * @return true, remove entire row, false, include the row (maybe).
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract public boolean filterRowKey(byte[] buffer, int offset, int length) throws IOException;

  /**
   * If this returns true, the scan will terminate.
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @return true to end scan, false to continue.
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract public boolean filterAllRemaining() throws IOException;

  /**
   * A way to filter based on the column family, column qualifier and/or the column value. Return
   * code is described below. This allows filters to filter only certain number of columns, then
   * terminate without matching ever column.
   *
   * If filterRowKey returns true, filterKeyValue needs to be consistent with it.
   *
   * filterKeyValue can assume that filterRowKey has already been called for the row.
   *
   * If your filter returns <code>ReturnCode.NEXT_ROW</code>, it should return
   * <code>ReturnCode.NEXT_ROW</code> until {@link #reset()} is called just in case the caller calls
   * for the next row.
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @param v the Cell in question
   * @return code as described below
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   * @see Filter.ReturnCode
   */
  abstract public ReturnCode filterKeyValue(final Cell v) throws IOException;

  /**
   * Give the filter a chance to transform the passed KeyValue. If the Cell is changed a new
   * Cell object must be returned.
   *
   * @see org.apache.hadoop.hbase.KeyValue#shallowCopy()
   *      The transformed KeyValue is what is eventually returned to the client. Most filters will
   *      return the passed KeyValue unchanged.
   * @see org.apache.hadoop.hbase.filter.KeyOnlyFilter#transform(KeyValue) for an example of a
   *      transformation.
   *
   *      Concrete implementers can signal a failure condition in their code by throwing an
   *      {@link IOException}.
   *
   * @param v the KeyValue in question
   * @return the changed KeyValue
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract public Cell transformCell(final Cell v) throws IOException;

  /**
   * WARNING: please to not override this method.  Instead override {@link #transformCell(Cell)}.
   * This is for transition from 0.94 -&gt; 0.96
   **/
  @Deprecated // use Cell transformCell(final Cell)
  abstract public KeyValue transform(final KeyValue currentKV) throws IOException;


  /**
   * Return codes for filterValue().
   */
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public enum ReturnCode {
    /**
     * Include the Cell
     */
    INCLUDE,
    /**
     * Include the Cell and seek to the next column skipping older versions.
     */
    INCLUDE_AND_NEXT_COL,
    /**
     * Skip this Cell
     */
    SKIP,
    /**
     * Skip this column. Go to the next column in this row.
     */
    NEXT_COL,
    /**
     * Seek to next row in current family. It may still pass a cell whose family is different but
     * row is the same as previous cell to {@link #filterKeyValue(Cell)} , even if we get a NEXT_ROW
     * returned for previous cell. For more details see HBASE-18368. <br>
     * Once reset() method was invoked, then we switch to the next row for all family, and you can
     * catch the event by invoking CellUtils.matchingRows(previousCell, currentCell). <br>
     * Note that filterRow() will still be called. <br>
     */
    NEXT_ROW,
    /**
     * Seek to next key which is given as hint by the filter.
     */
    SEEK_NEXT_USING_HINT,
    /**
     * Include KeyValue and done with row, seek to next. See NEXT_ROW
     */
    INCLUDE_AND_SEEK_NEXT_ROW,
  }

  /**
   * Chance to alter the list of Cells to be submitted. Modifications to the list will carry on
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @param kvs the list of Cells to be filtered
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract public void filterRowCells(List<Cell> kvs) throws IOException;

  /**
   * Primarily used to check for conflicts with scans(such as scans that do not read a full row at a
   * time).
   *
   * @return True if this filter actively uses filterRowCells(List) or filterRow().
   */
  abstract public boolean hasFilterRow();

  /**
   * Last chance to veto row based on previous {@link #filterKeyValue(Cell)} calls. The filter
   * needs to retain state then return a particular value for this call if they wish to exclude a
   * row if a certain column is missing (for example).
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @return true to exclude row, false to include row.
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract public boolean filterRow() throws IOException;

  /**
   * @param currentKV
   * @return KeyValue which must be next seeked. return null if the filter is not sure which key to
   *         seek to next.
   * @throws IOException
   * Function is Deprecated. Use {@link #getNextCellHint(Cell)} instead.
   */
  @Deprecated
  abstract public KeyValue getNextKeyHint(final KeyValue currentKV) throws IOException;

  /**
   * If the filter returns the match code SEEK_NEXT_USING_HINT, then it should also tell which is
   * the next key it must seek to. After receiving the match code SEEK_NEXT_USING_HINT, the
   * QueryMatcher would call this function to find out which key it must next seek to.
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @return KeyValue which must be next seeked. return null if the filter is not sure which key to
   *         seek to next.
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract public Cell getNextCellHint(final Cell currentKV) throws IOException;

  /**
   * Check that given column family is essential for filter to check row. Most filters always return
   * true here. But some could have more sophisticated logic which could significantly reduce
   * scanning process by not even touching columns until we are 100% sure that it's data is needed
   * in result.
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract public boolean isFamilyEssential(byte[] name) throws IOException;

  /**
   * TODO: JAVADOC
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @return The filter serialized using pb
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract public byte[] toByteArray() throws IOException;

  /**
   *
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @param pbBytes A pb serialized {@link Filter} instance
   * @return An instance of {@link Filter} made from <code>bytes</code>
   * @throws DeserializationException
   * @see #toByteArray
   */
  public static Filter parseFrom(final byte [] pbBytes) throws DeserializationException {
    throw new DeserializationException(
      "parseFrom called on base Filter, but should be called on derived type");
  }

  /**
   * Concrete implementers can signal a failure condition in their code by throwing an
   * {@link IOException}.
   *
   * @param other
   * @return true if and only if the fields of the filter that are serialized are equal to the
   *         corresponding fields in other. Used for testing.
   * @throws IOException in case an I/O or an filter specific failure needs to be signaled.
   */
  abstract boolean areSerializedFieldsEqual(Filter other);

  /**
   * alter the reversed scan flag
   * @param reversed flag
   */
  public void setReversed(boolean reversed) {
    this.reversed = reversed;
  }

  public boolean isReversed() {
    return this.reversed;
  }
}