Scan

/*
 *
 * 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.client;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.NavigableSet;
import java.util.TreeMap;
import java.util.TreeSet;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.classification.InterfaceStability;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.client.metrics.ScanMetrics;
import org.apache.hadoop.hbase.filter.Filter;
import org.apache.hadoop.hbase.filter.IncompatibleFilterException;
import org.apache.hadoop.hbase.io.TimeRange;
import org.apache.hadoop.hbase.protobuf.ProtobufUtil;
import org.apache.hadoop.hbase.security.access.Permission;
import org.apache.hadoop.hbase.security.visibility.Authorizations;
import org.apache.hadoop.hbase.util.Bytes;

/**
 * Used to perform Scan operations.
 * <p>
 * All operations are identical to {@link Get} with the exception of
 * instantiation.  Rather than specifying a single row, an optional startRow
 * and stopRow may be defined.  If rows are not specified, the Scanner will
 * iterate over all rows.
 * <p>
 * To get all columns from all rows of a Table, create an instance with no constraints; use the
 * {@link #Scan()} constructor. To constrain the scan to specific column families,
 * call {@link #addFamily(byte[]) addFamily} for each family to retrieve on your Scan instance.
 * <p>
 * To get specific columns, call {@link #addColumn(byte[], byte[]) addColumn}
 * for each column to retrieve.
 * <p>
 * To only retrieve columns within a specific range of version timestamps,
 * call {@link #setTimeRange(long, long) setTimeRange}.
 * <p>
 * To only retrieve columns with a specific timestamp, call
 * {@link #setTimeStamp(long) setTimestamp}.
 * <p>
 * To limit the number of versions of each column to be returned, call
 * {@link #setMaxVersions(int) setMaxVersions}.
 * <p>
 * To limit the maximum number of values returned for each call to next(),
 * call {@link #setBatch(int) setBatch}.
 * <p>
 * To add a filter, call {@link #setFilter(org.apache.hadoop.hbase.filter.Filter) setFilter}.
 * <p>
 * Expert: To explicitly disable server-side block caching for this scan,
 * execute {@link #setCacheBlocks(boolean)}.
 * <p><em>Note:</em> Usage alters Scan instances. Internally, attributes are updated as the Scan
 * runs and if enabled, metrics accumulate in the Scan instance. Be aware this is the case when
 * you go to clone a Scan instance or if you go to reuse a created Scan instance; safer is create
 * a Scan instance per usage.
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class Scan extends Query {
  private static final Log LOG = LogFactory.getLog(Scan.class);

  private static final String RAW_ATTR = "_raw_";

  private byte [] startRow = HConstants.EMPTY_START_ROW;
  private byte [] stopRow  = HConstants.EMPTY_END_ROW;
  private int maxVersions = 1;
  private int batch = -1;

  /**
   * Partial {@link Result}s are {@link Result}s must be combined to form a complete {@link Result}.
   * The {@link Result}s had to be returned in fragments (i.e. as partials) because the size of the
   * cells in the row exceeded max result size on the server. Typically partial results will be
   * combined client side into complete results before being delivered to the caller. However, if
   * this flag is set, the caller is indicating that they do not mind seeing partial results (i.e.
   * they understand that the results returned from the Scanner may only represent part of a
   * particular row). In such a case, any attempt to combine the partials into a complete result on
   * the client side will be skipped, and the caller will be able to see the exact results returned
   * from the server.
   */
  private boolean allowPartialResults = false;

  private int storeLimit = -1;
  private int storeOffset = 0;
  private boolean getScan;

  /**
   * @deprecated since 1.0.0. Use {@link #setScanMetricsEnabled(boolean)}
   */
  // Make private or remove.
  @Deprecated
  static public final String SCAN_ATTRIBUTES_METRICS_ENABLE = "scan.attributes.metrics.enable";

  /**
   * Use {@link #getScanMetrics()}
   */
  // Make this private or remove.
  @Deprecated
  static public final String SCAN_ATTRIBUTES_METRICS_DATA = "scan.attributes.metrics.data";

  // If an application wants to use multiple scans over different tables each scan must
  // define this attribute with the appropriate table name by calling
  // scan.setAttribute(Scan.SCAN_ATTRIBUTES_TABLE_NAME, Bytes.toBytes(tableName))
  static public final String SCAN_ATTRIBUTES_TABLE_NAME = "scan.attributes.table.name";

  /**
   * @deprecated without replacement
   *             This is now a no-op, SEEKs and SKIPs are optimizated automatically.
   *             Will be removed in 2.0+
   */
  @Deprecated
  public static final String HINT_LOOKAHEAD = "_look_ahead_";

  /*
   * -1 means no caching
   */
  private int caching = -1;
  private long maxResultSize = -1;
  private boolean cacheBlocks = true;
  private boolean reversed = false;
  private TimeRange tr = new TimeRange();
  private Map<byte [], NavigableSet<byte []>> familyMap =
    new TreeMap<byte [], NavigableSet<byte []>>(Bytes.BYTES_COMPARATOR);
  private Boolean loadColumnFamiliesOnDemand = null;

  /**
   * Set it true for small scan to get better performance
   *
   * Small scan should use pread and big scan can use seek + read
   *
   * seek + read is fast but can cause two problem (1) resource contention (2)
   * cause too much network io
   *
   * [89-fb] Using pread for non-compaction read request
   * https://issues.apache.org/jira/browse/HBASE-7266
   *
   * On the other hand, if setting it true, we would do
   * openScanner,next,closeScanner in one RPC call. It means the better
   * performance for small scan. [HBASE-9488].
   *
   * Generally, if the scan range is within one data block(64KB), it could be
   * considered as a small scan.
   */
  private boolean small = false;

  /**
   * Create a Scan operation across all rows.
   */
  public Scan() {}

  public Scan(byte [] startRow, Filter filter) {
    this(startRow);
    this.filter = filter;
  }

  /**
   * Create a Scan operation starting at the specified row.
   * <p>
   * If the specified row does not exist, the Scanner will start from the
   * next closest row after the specified row.
   * @param startRow row to start scanner at or after
   */
  public Scan(byte [] startRow) {
    this.startRow = startRow;
  }

  /**
   * Create a Scan operation for the range of rows specified.
   * @param startRow row to start scanner at or after (inclusive)
   * @param stopRow row to stop scanner before (exclusive)
   */
  public Scan(byte [] startRow, byte [] stopRow) {
    this.startRow = startRow;
    this.stopRow = stopRow;
    //if the startRow and stopRow both are empty, it is not a Get
    this.getScan = isStartRowAndEqualsStopRow();
  }

  /**
   * Creates a new instance of this class while copying all values.
   *
   * @param scan  The scan instance to copy from.
   * @throws IOException When copying the values fails.
   */
  public Scan(Scan scan) throws IOException {
    startRow = scan.getStartRow();
    stopRow  = scan.getStopRow();
    maxVersions = scan.getMaxVersions();
    batch = scan.getBatch();
    storeLimit = scan.getMaxResultsPerColumnFamily();
    storeOffset = scan.getRowOffsetPerColumnFamily();
    caching = scan.getCaching();
    maxResultSize = scan.getMaxResultSize();
    cacheBlocks = scan.getCacheBlocks();
    getScan = scan.isGetScan();
    filter = scan.getFilter(); // clone?
    loadColumnFamiliesOnDemand = scan.getLoadColumnFamiliesOnDemandValue();
    consistency = scan.getConsistency();
    this.setIsolationLevel(scan.getIsolationLevel());
    reversed = scan.isReversed();
    small = scan.isSmall();
    allowPartialResults = scan.getAllowPartialResults();
    TimeRange ctr = scan.getTimeRange();
    tr = new TimeRange(ctr.getMin(), ctr.getMax());
    Map<byte[], NavigableSet<byte[]>> fams = scan.getFamilyMap();
    for (Map.Entry<byte[],NavigableSet<byte[]>> entry : fams.entrySet()) {
      byte [] fam = entry.getKey();
      NavigableSet<byte[]> cols = entry.getValue();
      if (cols != null && cols.size() > 0) {
        for (byte[] col : cols) {
          addColumn(fam, col);
        }
      } else {
        addFamily(fam);
      }
    }
    for (Map.Entry<String, byte[]> attr : scan.getAttributesMap().entrySet()) {
      setAttribute(attr.getKey(), attr.getValue());
    }
    for (Map.Entry<byte[], TimeRange> entry : scan.getColumnFamilyTimeRange().entrySet()) {
      TimeRange tr = entry.getValue();
      setColumnFamilyTimeRange(entry.getKey(), tr.getMin(), tr.getMax());
    }
  }

  /**
   * Builds a scan object with the same specs as get.
   * @param get get to model scan after
   */
  public Scan(Get get) {
    this.startRow = get.getRow();
    this.stopRow = get.getRow();
    this.filter = get.getFilter();
    this.cacheBlocks = get.getCacheBlocks();
    this.maxVersions = get.getMaxVersions();
    this.storeLimit = get.getMaxResultsPerColumnFamily();
    this.storeOffset = get.getRowOffsetPerColumnFamily();
    this.tr = get.getTimeRange();
    this.familyMap = get.getFamilyMap();
    this.getScan = true;
    this.consistency = get.getConsistency();
    this.setIsolationLevel(get.getIsolationLevel());
    for (Map.Entry<String, byte[]> attr : get.getAttributesMap().entrySet()) {
      setAttribute(attr.getKey(), attr.getValue());
    }
    for (Map.Entry<byte[], TimeRange> entry : get.getColumnFamilyTimeRange().entrySet()) {
      TimeRange tr = entry.getValue();
      setColumnFamilyTimeRange(entry.getKey(), tr.getMin(), tr.getMax());
    }
  }

  public boolean isGetScan() {
    return this.getScan || isStartRowAndEqualsStopRow();
  }

  private boolean isStartRowAndEqualsStopRow() {
    return this.startRow != null && this.startRow.length > 0 &&
        Bytes.equals(this.startRow, this.stopRow);
  }
  /**
   * Get all columns from the specified family.
   * <p>
   * Overrides previous calls to addColumn for this family.
   * @param family family name
   * @return this
   */
  public Scan addFamily(byte [] family) {
    familyMap.remove(family);
    familyMap.put(family, null);
    return this;
  }

  /**
   * Get the column from the specified family with the specified qualifier.
   * <p>
   * Overrides previous calls to addFamily for this family.
   * @param family family name
   * @param qualifier column qualifier
   * @return this
   */
  public Scan addColumn(byte [] family, byte [] qualifier) {
    NavigableSet<byte []> set = familyMap.get(family);
    if(set == null) {
      set = new TreeSet<byte []>(Bytes.BYTES_COMPARATOR);
    }
    if (qualifier == null) {
      qualifier = HConstants.EMPTY_BYTE_ARRAY;
    }
    set.add(qualifier);
    familyMap.put(family, set);
    return this;
  }

  /**
   * Get versions of columns only within the specified timestamp range,
   * [minStamp, maxStamp).  Note, default maximum versions to return is 1.  If
   * your time range spans more than one version and you want all versions
   * returned, up the number of versions beyond the default.
   * @param minStamp minimum timestamp value, inclusive
   * @param maxStamp maximum timestamp value, exclusive
   * @see #setMaxVersions()
   * @see #setMaxVersions(int)
   * @return this
   */
  public Scan setTimeRange(long minStamp, long maxStamp) throws IOException {
    tr = new TimeRange(minStamp, maxStamp);
    return this;
  }

  /**
   * Get versions of columns with the specified timestamp. Note, default maximum
   * versions to return is 1.  If your time range spans more than one version
   * and you want all versions returned, up the number of versions beyond the
   * defaut.
   * @param timestamp version timestamp
   * @see #setMaxVersions()
   * @see #setMaxVersions(int)
   * @return this
   */
  public Scan setTimeStamp(long timestamp)
  throws IOException {
    try {
      tr = new TimeRange(timestamp, timestamp+1);
    } catch(Exception e) {
      // This should never happen, unless integer overflow or something extremely wrong...
      LOG.error("TimeRange failed, likely caused by integer overflow. ", e);
      throw e;
    }
    return this;
  }

  @Override public Scan setColumnFamilyTimeRange(byte[] cf, long minStamp, long maxStamp) {
    return (Scan) super.setColumnFamilyTimeRange(cf, minStamp, maxStamp);
  }

  /**
   * Set the start row of the scan.
   * @param startRow row to start scan on (inclusive)
   * Note: In order to make startRow exclusive add a trailing 0 byte
   * @return this
   */
  public Scan setStartRow(byte [] startRow) {
    this.startRow = startRow;
    return this;
  }

  /**
   * Set the stop row.
   * @param stopRow row to end at (exclusive)
   * <p><b>Note:</b> In order to make stopRow inclusive add a trailing 0 byte</p>
   * <p><b>Note:</b> When doing a filter for a rowKey <u>Prefix</u>
   * use {@link #setRowPrefixFilter(byte[])}.
   * The 'trailing 0' will not yield the desired result.</p>
   * @return this
   */
  public Scan setStopRow(byte [] stopRow) {
    this.stopRow = stopRow;
    return this;
  }

  /**
   * <p>Set a filter (using stopRow and startRow) so the result set only contains rows where the
   * rowKey starts with the specified prefix.</p>
   * <p>This is a utility method that converts the desired rowPrefix into the appropriate values
   * for the startRow and stopRow to achieve the desired result.</p>
   * <p>This can safely be used in combination with setFilter.</p>
   * <p><b>NOTE: Doing a {@link #setStartRow(byte[])} and/or {@link #setStopRow(byte[])}
   * after this method will yield undefined results.</b></p>
   * @param rowPrefix the prefix all rows must start with. (Set <i>null</i> to remove the filter.)
   * @return this
   */
  public Scan setRowPrefixFilter(byte[] rowPrefix) {
    if (rowPrefix == null) {
      setStartRow(HConstants.EMPTY_START_ROW);
      setStopRow(HConstants.EMPTY_END_ROW);
    } else {
      this.setStartRow(rowPrefix);
      this.setStopRow(calculateTheClosestNextRowKeyForPrefix(rowPrefix));
    }
    return this;
  }

  /**
   * <p>When scanning for a prefix the scan should stop immediately after the the last row that
   * has the specified prefix. This method calculates the closest next rowKey immediately following
   * the given rowKeyPrefix.</p>
   * <p><b>IMPORTANT: This converts a rowKey<u>Prefix</u> into a rowKey</b>.</p>
   * <p>If the prefix is an 'ASCII' string put into a byte[] then this is easy because you can
   * simply increment the last byte of the array.
   * But if your application uses real binary rowids you may run into the scenario that your
   * prefix is something like:</p>
   * &nbsp;&nbsp;&nbsp;<b>{ 0x12, 0x23, 0xFF, 0xFF }</b><br/>
   * Then this stopRow needs to be fed into the actual scan<br/>
   * &nbsp;&nbsp;&nbsp;<b>{ 0x12, 0x24 }</b> (Notice that it is shorter now)<br/>
   * This method calculates the correct stop row value for this usecase.
   *
   * @param rowKeyPrefix the rowKey<u>Prefix</u>.
   * @return the closest next rowKey immediately following the given rowKeyPrefix.
   */
  private byte[] calculateTheClosestNextRowKeyForPrefix(byte[] rowKeyPrefix) {
    // Essentially we are treating it like an 'unsigned very very long' and doing +1 manually.
    // Search for the place where the trailing 0xFFs start
    int offset = rowKeyPrefix.length;
    while (offset > 0) {
      if (rowKeyPrefix[offset - 1] != (byte) 0xFF) {
        break;
      }
      offset--;
    }

    if (offset == 0) {
      // We got an 0xFFFF... (only FFs) stopRow value which is
      // the last possible prefix before the end of the table.
      // So set it to stop at the 'end of the table'
      return HConstants.EMPTY_END_ROW;
    }

    // Copy the right length of the original
    byte[] newStopRow = Arrays.copyOfRange(rowKeyPrefix, 0, offset);
    // And increment the last one
    newStopRow[newStopRow.length - 1]++;
    return newStopRow;
  }

  /**
   * Get all available versions.
   * @return this
   */
  public Scan setMaxVersions() {
    this.maxVersions = Integer.MAX_VALUE;
    return this;
  }

  /**
   * Get up to the specified number of versions of each column.
   * @param maxVersions maximum versions for each column
   * @return this
   */
  public Scan setMaxVersions(int maxVersions) {
    this.maxVersions = maxVersions;
    return this;
  }

  /**
   * Set the maximum number of values to return for each call to next()
   * @param batch the maximum number of values
   */
  public Scan setBatch(int batch) {
    if (this.hasFilter() && this.filter.hasFilterRow()) {
      throw new IncompatibleFilterException(
        "Cannot set batch on a scan using a filter" +
        " that returns true for filter.hasFilterRow");
    }
    this.batch = batch;
    return this;
  }

  /**
   * Set the maximum number of values to return per row per Column Family
   * @param limit the maximum number of values returned / row / CF
   */
  public Scan setMaxResultsPerColumnFamily(int limit) {
    this.storeLimit = limit;
    return this;
  }

  /**
   * Set offset for the row per Column Family.
   * @param offset is the number of kvs that will be skipped.
   */
  public Scan setRowOffsetPerColumnFamily(int offset) {
    this.storeOffset = offset;
    return this;
  }

  /**
   * Set the number of rows for caching that will be passed to scanners.
   * If not set, the Configuration setting {@link HConstants#HBASE_CLIENT_SCANNER_CACHING} will
   * apply.
   * Higher caching values will enable faster scanners but will use more memory.
   * @param caching the number of rows for caching
   */
  public Scan setCaching(int caching) {
    this.caching = caching;
    return this;
  }

  /**
   * @return the maximum result size in bytes. See {@link #setMaxResultSize(long)}
   */
  public long getMaxResultSize() {
    return maxResultSize;
  }

  /**
   * Set the maximum result size. The default is -1; this means that no specific
   * maximum result size will be set for this scan, and the global configured
   * value will be used instead. (Defaults to unlimited).
   *
   * @param maxResultSize The maximum result size in bytes.
   */
  public Scan setMaxResultSize(long maxResultSize) {
    this.maxResultSize = maxResultSize;
    return this;
  }

  @Override
  public Scan setFilter(Filter filter) {
    super.setFilter(filter);
    return this;
  }

  /**
   * Setting the familyMap
   * @param familyMap map of family to qualifier
   * @return this
   */
  public Scan setFamilyMap(Map<byte [], NavigableSet<byte []>> familyMap) {
    this.familyMap = familyMap;
    return this;
  }

  /**
   * Getting the familyMap
   * @return familyMap
   */
  public Map<byte [], NavigableSet<byte []>> getFamilyMap() {
    return this.familyMap;
  }

  /**
   * @return the number of families in familyMap
   */
  public int numFamilies() {
    if(hasFamilies()) {
      return this.familyMap.size();
    }
    return 0;
  }

  /**
   * @return true if familyMap is non empty, false otherwise
   */
  public boolean hasFamilies() {
    return !this.familyMap.isEmpty();
  }

  /**
   * @return the keys of the familyMap
   */
  public byte[][] getFamilies() {
    if(hasFamilies()) {
      return this.familyMap.keySet().toArray(new byte[0][0]);
    }
    return null;
  }

  /**
   * @return the startrow
   */
  public byte [] getStartRow() {
    return this.startRow;
  }

  /**
   * @return the stoprow
   */
  public byte [] getStopRow() {
    return this.stopRow;
  }

  /**
   * @return the max number of versions to fetch
   */
  public int getMaxVersions() {
    return this.maxVersions;
  }

  /**
   * @return maximum number of values to return for a single call to next()
   */
  public int getBatch() {
    return this.batch;
  }

  /**
   * @return maximum number of values to return per row per CF
   */
  public int getMaxResultsPerColumnFamily() {
    return this.storeLimit;
  }

  /**
   * Method for retrieving the scan's offset per row per column
   * family (#kvs to be skipped)
   * @return row offset
   */
  public int getRowOffsetPerColumnFamily() {
    return this.storeOffset;
  }

  /**
   * @return caching the number of rows fetched when calling next on a scanner
   */
  public int getCaching() {
    return this.caching;
  }

  /**
   * @return TimeRange
   */
  public TimeRange getTimeRange() {
    return this.tr;
  }

  /**
   * @return RowFilter
   */
  @Override
  public Filter getFilter() {
    return filter;
  }

  /**
   * @return true is a filter has been specified, false if not
   */
  public boolean hasFilter() {
    return filter != null;
  }

  /**
   * Set whether blocks should be cached for this Scan.
   * <p>
   * This is true by default.  When true, default settings of the table and
   * family are used (this will never override caching blocks if the block
   * cache is disabled for that family or entirely).
   *
   * @param cacheBlocks if false, default settings are overridden and blocks
   * will not be cached
   */
  public Scan setCacheBlocks(boolean cacheBlocks) {
    this.cacheBlocks = cacheBlocks;
    return this;
  }

  /**
   * Get whether blocks should be cached for this Scan.
   * @return true if default caching should be used, false if blocks should not
   * be cached
   */
  public boolean getCacheBlocks() {
    return cacheBlocks;
  }

  /**
   * Set whether this scan is a reversed one
   * <p>
   * This is false by default which means forward(normal) scan.
   *
   * @param reversed if true, scan will be backward order
   * @return this
   */
  public Scan setReversed(boolean reversed) {
    this.reversed = reversed;
    return this;
  }

  /**
   * Get whether this scan is a reversed one.
   * @return true if backward scan, false if forward(default) scan
   */
  public boolean isReversed() {
    return reversed;
  }

  /**
   * Setting whether the caller wants to see the partial results that may be returned from the
   * server. By default this value is false and the complete results will be assembled client side
   * before being delivered to the caller.
   * @param allowPartialResults
   * @return this
   */
  public Scan setAllowPartialResults(final boolean allowPartialResults) {
    this.allowPartialResults = allowPartialResults;
    return this;
  }

  /**
   * @return true when the constructor of this scan understands that the results they will see may
   *         only represent a partial portion of a row. The entire row would be retrieved by
   *         subsequent calls to {@link ResultScanner#next()}
   */
  public boolean getAllowPartialResults() {
    return allowPartialResults;
  }

  /**
   * Set the value indicating whether loading CFs on demand should be allowed (cluster
   * default is false). On-demand CF loading doesn't load column families until necessary, e.g.
   * if you filter on one column, the other column family data will be loaded only for the rows
   * that are included in result, not all rows like in normal case.
   * With column-specific filters, like SingleColumnValueFilter w/filterIfMissing == true,
   * this can deliver huge perf gains when there's a cf with lots of data; however, it can
   * also lead to some inconsistent results, as follows:
   * - if someone does a concurrent update to both column families in question you may get a row
   *   that never existed, e.g. for { rowKey = 5, { cat_videos =&gt; 1 }, { video =&gt; "my cat" } }
   *   someone puts rowKey 5 with { cat_videos =&gt; 0 }, { video =&gt; "my dog" }, concurrent scan
   *   filtering on "cat_videos == 1" can get { rowKey = 5, { cat_videos =&gt; 1 },
   *   { video =&gt; "my dog" } }.
   * - if there's a concurrent split and you have more than 2 column families, some rows may be
   *   missing some column families.
   */
  public Scan setLoadColumnFamiliesOnDemand(boolean value) {
    this.loadColumnFamiliesOnDemand = value;
    return this;
  }

  /**
   * Get the raw loadColumnFamiliesOnDemand setting; if it's not set, can be null.
   */
  public Boolean getLoadColumnFamiliesOnDemandValue() {
    return this.loadColumnFamiliesOnDemand;
  }

  /**
   * Get the logical value indicating whether on-demand CF loading should be allowed.
   */
  public boolean doLoadColumnFamiliesOnDemand() {
    return (this.loadColumnFamiliesOnDemand != null)
      && this.loadColumnFamiliesOnDemand.booleanValue();
  }

  /**
   * Compile the table and column family (i.e. schema) information
   * into a String. Useful for parsing and aggregation by debugging,
   * logging, and administration tools.
   * @return Map
   */
  @Override
  public Map<String, Object> getFingerprint() {
    Map<String, Object> map = new HashMap<String, Object>();
    List<String> families = new ArrayList<String>();
    if(this.familyMap.size() == 0) {
      map.put("families", "ALL");
      return map;
    } else {
      map.put("families", families);
    }
    for (Map.Entry<byte [], NavigableSet<byte[]>> entry :
        this.familyMap.entrySet()) {
      families.add(Bytes.toStringBinary(entry.getKey()));
    }
    return map;
  }

  /**
   * Compile the details beyond the scope of getFingerprint (row, columns,
   * timestamps, etc.) into a Map along with the fingerprinted information.
   * Useful for debugging, logging, and administration tools.
   * @param maxCols a limit on the number of columns output prior to truncation
   * @return Map
   */
  @Override
  public Map<String, Object> toMap(int maxCols) {
    // start with the fingerpring map and build on top of it
    Map<String, Object> map = getFingerprint();
    // map from families to column list replaces fingerprint's list of families
    Map<String, List<String>> familyColumns =
      new HashMap<String, List<String>>();
    map.put("families", familyColumns);
    // add scalar information first
    map.put("startRow", Bytes.toStringBinary(this.startRow));
    map.put("stopRow", Bytes.toStringBinary(this.stopRow));
    map.put("maxVersions", this.maxVersions);
    map.put("batch", this.batch);
    map.put("caching", this.caching);
    map.put("maxResultSize", this.maxResultSize);
    map.put("cacheBlocks", this.cacheBlocks);
    map.put("loadColumnFamiliesOnDemand", this.loadColumnFamiliesOnDemand);
    List<Long> timeRange = new ArrayList<Long>();
    timeRange.add(this.tr.getMin());
    timeRange.add(this.tr.getMax());
    map.put("timeRange", timeRange);
    int colCount = 0;
    // iterate through affected families and list out up to maxCols columns
    for (Map.Entry<byte [], NavigableSet<byte[]>> entry :
      this.familyMap.entrySet()) {
      List<String> columns = new ArrayList<String>();
      familyColumns.put(Bytes.toStringBinary(entry.getKey()), columns);
      if(entry.getValue() == null) {
        colCount++;
        --maxCols;
        columns.add("ALL");
      } else {
        colCount += entry.getValue().size();
        if (maxCols <= 0) {
          continue;
        }
        for (byte [] column : entry.getValue()) {
          if (--maxCols <= 0) {
            continue;
          }
          columns.add(Bytes.toStringBinary(column));
        }
      }
    }
    map.put("totalColumns", colCount);
    if (this.filter != null) {
      map.put("filter", this.filter.toString());
    }
    // add the id if set
    if (getId() != null) {
      map.put("id", getId());
    }
    return map;
  }

  /**
   * Enable/disable "raw" mode for this scan.
   * If "raw" is enabled the scan will return all
   * delete marker and deleted rows that have not
   * been collected, yet.
   * This is mostly useful for Scan on column families
   * that have KEEP_DELETED_ROWS enabled.
   * It is an error to specify any column when "raw" is set.
   * @param raw True/False to enable/disable "raw" mode.
   */
  public Scan setRaw(boolean raw) {
    setAttribute(RAW_ATTR, Bytes.toBytes(raw));
    return this;
  }

  /**
   * @return True if this Scan is in "raw" mode.
   */
  public boolean isRaw() {
    byte[] attr = getAttribute(RAW_ATTR);
    return attr == null ? false : Bytes.toBoolean(attr);
  }


  /**
   * Set whether this scan is a small scan
   * <p>
   * Small scan should use pread and big scan can use seek + read
   *
   * seek + read is fast but can cause two problem (1) resource contention (2)
   * cause too much network io
   *
   * [89-fb] Using pread for non-compaction read request
   * https://issues.apache.org/jira/browse/HBASE-7266
   *
   * On the other hand, if setting it true, we would do
   * openScanner,next,closeScanner in one RPC call. It means the better
   * performance for small scan. [HBASE-9488].
   *
   * Generally, if the scan range is within one data block(64KB), it could be
   * considered as a small scan.
   *
   * @param small
   */
  public Scan setSmall(boolean small) {
    this.small = small;
    return this;
  }

  /**
   * Get whether this scan is a small scan
   * @return true if small scan
   */
  public boolean isSmall() {
    return small;
  }

  @Override
  public Scan setAttribute(String name, byte[] value) {
    return (Scan) super.setAttribute(name, value);
  }

  @Override
  public Scan setId(String id) {
    return (Scan) super.setId(id);
  }

  @Override
  public Scan setAuthorizations(Authorizations authorizations) {
    return (Scan) super.setAuthorizations(authorizations);
  }

  @Override
  public Scan setACL(Map<String, Permission> perms) {
    return (Scan) super.setACL(perms);
  }

  @Override
  public Scan setACL(String user, Permission perms) {
    return (Scan) super.setACL(user, perms);
  }

  @Override
  public Scan setConsistency(Consistency consistency) {
    return (Scan) super.setConsistency(consistency);
  }

  @Override
  public Scan setReplicaId(int Id) {
    return (Scan) super.setReplicaId(Id);
  }

  @Override
  public Scan setIsolationLevel(IsolationLevel level) {
    return (Scan) super.setIsolationLevel(level);
  }

  /**
   * Utility that creates a Scan that will do a  small scan in reverse from passed row
   * looking for next closest row.
   * @param row
   * @param family
   * @return An instance of Scan primed with passed <code>row</code> and <code>family</code> to
   * scan in reverse for one row only.
   */
  static Scan createGetClosestRowOrBeforeReverseScan(byte[] row) {
    // Below does not work if you add in family; need to add the family qualifier that is highest
    // possible family qualifier.  Do we have such a notion?  Would have to be magic.
    Scan scan = new Scan(row);
    scan.setSmall(true);
    scan.setReversed(true);
    scan.setCaching(1);
    return scan;
  }

  /**
   * Enable collection of {@link ScanMetrics}. For advanced users.
   * @param enabled Set to true to enable accumulating scan metrics
   */
  public Scan setScanMetricsEnabled(final boolean enabled) {
    setAttribute(Scan.SCAN_ATTRIBUTES_METRICS_ENABLE, Bytes.toBytes(Boolean.valueOf(enabled)));
    return this;
  }

  /**
   * @return True if collection of scan metrics is enabled. For advanced users.
   */
  public boolean isScanMetricsEnabled() {
    byte[] attr = getAttribute(Scan.SCAN_ATTRIBUTES_METRICS_ENABLE);
    return attr == null ? false : Bytes.toBoolean(attr);
  }

  /**
   * @return Metrics on this Scan, if metrics were enabled.
   * @see #setScanMetricsEnabled(boolean)
   */
  public ScanMetrics getScanMetrics() {
    byte [] bytes = getAttribute(Scan.SCAN_ATTRIBUTES_METRICS_DATA);
    if (bytes == null) return null;
    return ProtobufUtil.toScanMetrics(bytes);
  }
}