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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.Collection;
import java.util.Optional;
import java.util.OptionalInt;
import java.util.OptionalLong;

import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellComparator;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Utility functions for region server storage layer.
 */
@InterfaceAudience.Private
public class StoreUtils {

  private static final Logger LOG = LoggerFactory.getLogger(StoreUtils.class);

  /**
   * Creates a deterministic hash code for store file collection.
   */
  public static OptionalInt getDeterministicRandomSeed(Collection files) {
    return files.stream().mapToInt(f -> f.getPath().getName().hashCode()).findFirst();
  }

  /**
   * Determines whether any files in the collection are references.
   * @param files The files.
   */
  public static boolean hasReferences(Collection files) {
    // TODO: make sure that we won't pass null here in the future.
    return files != null && files.stream().anyMatch(HStoreFile::isReference);
  }

  /**
   * Gets lowest timestamp from candidate StoreFiles
   */
  public static long getLowestTimestamp(Collection candidates) throws IOException {
    long minTs = Long.MAX_VALUE;
    for (HStoreFile storeFile : candidates) {
      minTs = Math.min(minTs, storeFile.getModificationTimestamp());
    }
    return minTs;
  }

  /**
   * Gets the largest file (with reader) out of the list of files.
   * @param candidates The files to choose from.
   * @return The largest file; null if no file has a reader.
   */
  static Optional getLargestFile(Collection candidates) {
    return candidates.stream().filter(f -> f.getReader() != null)
        .max((f1, f2) -> Long.compare(f1.getReader().length(), f2.getReader().length()));
  }

  /**
   * Return the largest memstoreTS found across all storefiles in the given list. Store files that
   * were created by a mapreduce bulk load are ignored, as they do not correspond to any specific
   * put operation, and thus do not have a memstoreTS associated with them.
   */
  public static OptionalLong getMaxMemStoreTSInList(Collection sfs) {
    return sfs.stream().filter(sf -> !sf.isBulkLoadResult()).mapToLong(HStoreFile::getMaxMemStoreTS)
        .max();
  }

  /**
   * Return the highest sequence ID found across all storefiles in the given list.
   */
  public static OptionalLong getMaxSequenceIdInList(Collection sfs) {
    return sfs.stream().mapToLong(HStoreFile::getMaxSequenceId).max();
  }

  /**
   * Gets the approximate mid-point of the given file that is optimal for use in splitting it.
   * @param file the store file
   * @param comparator Comparator used to compare KVs.
   * @return The split point row, or null if splitting is not possible, or reader is null.
   */
  static Optional getFileSplitPoint(HStoreFile file, CellComparator comparator)
      throws IOException {
    StoreFileReader reader = file.getReader();
    if (reader == null) {
      LOG.warn("Storefile " + file + " Reader is null; cannot get split point");
      return Optional.empty();
    }
    // Get first, last, and mid keys. Midkey is the key that starts block
    // in middle of hfile. Has column and timestamp. Need to return just
    // the row we want to split on as midkey.
    Optional optionalMidKey = reader.midKey();
    if (!optionalMidKey.isPresent()) {
      return Optional.empty();
    }
    Cell midKey = optionalMidKey.get();
    Cell firstKey = reader.getFirstKey().get();
    Cell lastKey = reader.getLastKey().get();
    // if the midkey is the same as the first or last keys, we cannot (ever) split this region.
    if (comparator.compareRows(midKey, firstKey) == 0 ||
        comparator.compareRows(midKey, lastKey) == 0) {
      if (LOG.isDebugEnabled()) {
        LOG.debug("cannot split {} because midkey is the same as first or last row", file);
      }
      return Optional.empty();
    }
    return Optional.of(CellUtil.cloneRow(midKey));
  }

  /**
   * Gets the mid point of the largest file passed in as split point.
   */
  static Optional getSplitPoint(Collection storefiles,
      CellComparator comparator) throws IOException {
    Optional largestFile = StoreUtils.getLargestFile(storefiles);
    return largestFile.isPresent() ? StoreUtils.getFileSplitPoint(largestFile.get(), comparator)
        : Optional.empty();
  }
}