content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.master.journal.ufs;
  
  import alluxio.Constants;
  import alluxio.conf.Configuration;
  import alluxio.conf.PropertyKey;
  import alluxio.underfs.UnderFileSystem;
  import alluxio.util.ThreadFactoryUtils;
  
  import com.google.common.base.Preconditions;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.net.URI;
  import java.util.List;
  import java.util.concurrent.Executors;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.ScheduledFuture;
  import java.util.concurrent.TimeUnit;
  import javax.annotation.concurrent.ThreadSafe;
  
  /**
   * A garbage collector that periodically snapshots the journal and deletes files that are not
   * necessary anymore. The implementation guarantees that the journal contains all the information
   * required to recover the master full state.
   */
  @ThreadSafe
  final class UfsJournalGarbageCollector implements Closeable {
    private static final Logger LOG = LoggerFactory.getLogger(UfsJournalGarbageCollector.class);
  
    private final ScheduledExecutorService mExecutor = Executors.newSingleThreadScheduledExecutor(
        ThreadFactoryUtils.build("UfsJournalGarbageCollector-%d", true));
    private final UfsJournal mJournal;
    private final UnderFileSystem mUfs;
    private ScheduledFuture<?> mGc;
  
    /**
     * Creates the {@link UfsJournalGarbageCollector} instance.
     *
     * @param journal the UFS journal handle
     */
    UfsJournalGarbageCollector(UfsJournal journal) {
      mJournal = Preconditions.checkNotNull(journal, "journal");
      mUfs = mJournal.getUfs();
      mGc = mExecutor.scheduleAtFixedRate(this::gc,
          Constants.SECOND_MS, Configuration.getMs(PropertyKey.MASTER_JOURNAL_GC_PERIOD_MS),
          TimeUnit.MILLISECONDS);
    }
  
    @Override
    public void close() {
      if (mGc != null) {
        mGc.cancel(true);
        mGc = null;
      }
      mExecutor.shutdown();
    }
  
    /**
     * Deletes unneeded snapshots.
     */
    void gc() {
      UfsJournalSnapshot snapshot;
      try {
        snapshot = UfsJournalSnapshot.getSnapshot(mJournal);
      } catch (IOException e) {
        LOG.warn("Failed to get journal snapshot with error {}.", e.toString());
        return;
      }
      long checkpointSequenceNumber = 0;
  
      // Checkpoint.
      List<UfsJournalFile> checkpoints = snapshot.getCheckpoints();
      if (!checkpoints.isEmpty()) {
        checkpointSequenceNumber = checkpoints.get(checkpoints.size() - 1).getEnd();
      }
      for (int i = 0; i < checkpoints.size() - 1; i++) {
        // Only keep at most 2 checkpoints.
        if (i < checkpoints.size() - 2) {
          deleteNoException(checkpoints.get(i).getLocation());
        }
        // For the the second last checkpoint. Check whether it has been there for a long time.
        gcFileIfStale(checkpoints.get(i), checkpointSequenceNumber);
      }
  
      for (UfsJournalFile log : snapshot.getLogs()) {
        gcFileIfStale(log, checkpointSequenceNumber);
      }
  
      for (UfsJournalFile tmpCheckpoint : snapshot.getTemporaryCheckpoints()) {
        gcFileIfStale(tmpCheckpoint, checkpointSequenceNumber);
      }
    }
  
    /**
     * Garbage collects a file if necessary.
     *
     * @param file the file
     * @param checkpointSequenceNumber the first sequence number that has not been checkpointed
     */
    private void gcFileIfStale(UfsJournalFile file, long checkpointSequenceNumber) {
      if (file.getEnd() > checkpointSequenceNumber && !file.isTmpCheckpoint()) {
        return;
      }
  
      Long lastModifiedTimeMs;
      try {
        lastModifiedTimeMs = mUfs.getFileStatus(file.getLocation().toString()).getLastModifiedTime();
      } catch (IOException e) {
        LOG.warn("Failed to get the last modified time for {}.", file.getLocation());
        return;
      }
      if (lastModifiedTimeMs == null) {
        LOG.warn("Failed to get the last modified time for {}.", file.getLocation());
        return;
      }
  
      long thresholdMs = file.isTmpCheckpoint()
          ? Configuration.getMs(PropertyKey.MASTER_JOURNAL_TEMPORARY_FILE_GC_THRESHOLD_MS)
          : Configuration.getMs(PropertyKey.MASTER_JOURNAL_GC_THRESHOLD_MS);
  
      if (System.currentTimeMillis() - lastModifiedTimeMs > thresholdMs) {
        deleteNoException(file.getLocation());
      }
    }
  
    /**
     * Deletes a file and swallows the exception by logging it.
     *
     * @param location the file location
     */
    private void deleteNoException(URI location) {
      try {
        mUfs.deleteFile(location.toString());
        LOG.info("Garbage collected journal file {}.", location);
      } catch (IOException e) {
        LOG.warn("Failed to garbage collect journal file {}.", location);
      }
    }
  }
  