HADOOP-17023. Tune S3AFileSystem.listStatus() (#2257)

S3AFileSystem.listStatus() is optimized for invocations
where the path supplied is a non-empty directory.
The number of S3 requests is significantly reduced, saving
time, money, and reducing the risk of S3 throttling.

Contributed by Mukund Thakur.

Change-Id: I7cc5f87aa16a4819e245e0fbd2aad226bd500f3f

Author: mukund-thakur

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/Listing.java

@@ -24,6 +24,7 @@
 import com.amazonaws.services.s3.model.S3ObjectSummary;
 import com.google.common.annotations.VisibleForTesting;
 
+import org.apache.commons.lang3.tuple.Triple;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.LocatedFileStatus;
@@ -102,6 +103,19 @@ ProvidedFileStatusIterator createProvidedFileStatusIterator(
     return new ProvidedFileStatusIterator(fileStatuses, filter, acceptor);
   }
 
+  /**
+   * Create a FileStatus iterator against a provided list of file status.
+   * @param fileStatuses array of file status.
+   * @return the file status iterator.
+   */
+  @VisibleForTesting
+  public static ProvidedFileStatusIterator toProvidedFileStatusIterator(
+          S3AFileStatus[] fileStatuses) {
+    return new ProvidedFileStatusIterator(fileStatuses,
+            ACCEPT_ALL,
+            Listing.ACCEPT_ALL_BUT_S3N);
+  }
+
   /**
    * Create a FileStatus iterator against a path, with a given list object
    * request.
@@ -250,7 +264,7 @@ public RemoteIterator<S3ALocatedFileStatus> getListFilesAssumingDir(
       if (!forceNonAuthoritativeMS &&
               allowAuthoritative &&
               metadataStoreListFilesIterator.isRecursivelyAuthoritative()) {
-        S3AFileStatus[] statuses = S3Guard.iteratorToStatuses(
+        S3AFileStatus[] statuses = S3AUtils.iteratorToStatuses(
                 metadataStoreListFilesIterator, tombstones);
         cachedFilesIterator = createProvidedFileStatusIterator(
                 statuses, ACCEPT_ALL, acceptor);
@@ -329,6 +343,56 @@ public RemoteIterator<S3ALocatedFileStatus> getLocatedFileStatusIteratorForDir(
             tombstones);
   }
 
+  /**
+   * Calculate list of file statuses assuming path
+   * to be a non-empty directory.
+   * @param path input path.
+   * @return Triple of file statuses, metaData, auth flag.
+   * @throws IOException Any IO problems.
+   */
+  public Triple<RemoteIterator<S3AFileStatus>, DirListingMetadata, Boolean>
+        getFileStatusesAssumingNonEmptyDir(Path path)
+          throws IOException {
+    String key = pathToKey(path);
+    List<S3AFileStatus> result;
+    if (!key.isEmpty()) {
+      key = key + '/';
+    }
+
+    boolean allowAuthoritative = listingOperationCallbacks
+            .allowAuthoritative(path);
+    DirListingMetadata dirMeta =
+            S3Guard.listChildrenWithTtl(
+                    getStoreContext().getMetadataStore(),
+                    path,
+                    listingOperationCallbacks.getUpdatedTtlTimeProvider(),
+                    allowAuthoritative);
+    // In auth mode return directly with auth flag.
+    if (allowAuthoritative && dirMeta != null && dirMeta.isAuthoritative()) {
+      ProvidedFileStatusIterator mfsItr = createProvidedFileStatusIterator(
+              S3Guard.dirMetaToStatuses(dirMeta),
+              ACCEPT_ALL,
+              Listing.ACCEPT_ALL_BUT_S3N);
+      return Triple.of(mfsItr,
+              dirMeta, Boolean.TRUE);
+    }
+
+    S3ListRequest request = createListObjectsRequest(key, "/");
+    LOG.debug("listStatus: doing listObjects for directory {}", key);
+
+    FileStatusListingIterator filesItr = createFileStatusListingIterator(
+            path,
+            request,
+            ACCEPT_ALL,
+            new Listing.AcceptAllButSelfAndS3nDirs(path));
+
+    // return the results obtained from s3.
+    return Triple.of(
+            filesItr,
+            dirMeta,
+            Boolean.FALSE);
+  }
+
   public S3ListRequest createListObjectsRequest(String key, String delimiter) {
     return listingOperationCallbacks.createListObjectsRequest(key, delimiter);
   }

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java

@@ -35,6 +35,7 @@
 import java.util.Collections;
 import java.util.Date;
 import java.util.EnumSet;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -185,6 +186,7 @@
 import static org.apache.hadoop.fs.s3a.impl.InternalConstants.SC_404;
 import static org.apache.hadoop.fs.s3a.impl.NetworkBinding.fixBucketRegion;
 import static org.apache.hadoop.fs.s3a.impl.NetworkBinding.logDnsLookup;
+import static org.apache.hadoop.fs.s3a.s3guard.S3Guard.dirMetaToStatuses;
 import static org.apache.hadoop.io.IOUtils.cleanupWithLogger;
 
 /**
@@ -2652,7 +2654,9 @@ void maybeCreateFakeParentDirectory(Path path)
    */
   public FileStatus[] listStatus(Path f) throws FileNotFoundException,
       IOException {
-    return once("listStatus", f.toString(), () -> innerListStatus(f));
+    return once("listStatus",
+        f.toString(),
+        () -> iteratorToStatuses(innerListStatus(f), new HashSet<>()));
   }
 
   /**
@@ -2665,51 +2669,52 @@ public FileStatus[] listStatus(Path f) throws FileNotFoundException,
    * @throws IOException due to an IO problem.
    * @throws AmazonClientException on failures inside the AWS SDK
    */
-  private S3AFileStatus[] innerListStatus(Path f) throws FileNotFoundException,
-      IOException, AmazonClientException {
+  private RemoteIterator<S3AFileStatus> innerListStatus(Path f)
+          throws FileNotFoundException,
+          IOException, AmazonClientException {
     Path path = qualify(f);
-    String key = pathToKey(path);
     LOG.debug("List status for path: {}", path);
     entryPoint(INVOCATION_LIST_STATUS);
 
-    List<S3AFileStatus> result;
-    final S3AFileStatus fileStatus = innerGetFileStatus(path, false,
-        StatusProbeEnum.ALL);
-
-    if (fileStatus.isDirectory()) {
-      if (!key.isEmpty()) {
-        key = key + '/';
+    Triple<RemoteIterator<S3AFileStatus>, DirListingMetadata, Boolean>
+            statusesAssumingNonEmptyDir = listing
+            .getFileStatusesAssumingNonEmptyDir(path);
+
+    if (!statusesAssumingNonEmptyDir.getLeft().hasNext() &&
+            statusesAssumingNonEmptyDir.getRight()) {
+      // We are sure that this is an empty directory in auth mode.
+      return statusesAssumingNonEmptyDir.getLeft();
+    } else if (!statusesAssumingNonEmptyDir.getLeft().hasNext()) {
+      // We may have an empty dir, or may have file or may have nothing.
+      // So we call innerGetFileStatus to get the status, this may throw
+      // FileNotFoundException if we have nothing.
+      // So We are guaranteed to have either a dir marker or a file.
+      final S3AFileStatus fileStatus = innerGetFileStatus(path, false,
+              StatusProbeEnum.ALL);
+      // If it is a file return directly.
+      if (fileStatus.isFile()) {
+        LOG.debug("Adding: rd (not a dir): {}", path);
+        S3AFileStatus[] stats = new S3AFileStatus[1];
+        stats[0] = fileStatus;
+        return listing.createProvidedFileStatusIterator(
+                stats,
+                ACCEPT_ALL,
+                Listing.ACCEPT_ALL_BUT_S3N);
       }
-
-      boolean allowAuthoritative = allowAuthoritative(f);
-      DirListingMetadata dirMeta =
-          S3Guard.listChildrenWithTtl(metadataStore, path, ttlTimeProvider,
-              allowAuthoritative);
-      if (allowAuthoritative && dirMeta != null && dirMeta.isAuthoritative()) {
-        return S3Guard.dirMetaToStatuses(dirMeta);
-      }
-
-      S3ListRequest request = createListObjectsRequest(key, "/");
-      LOG.debug("listStatus: doing listObjects for directory {}", key);
-
-      Listing.FileStatusListingIterator files =
-          listing.createFileStatusListingIterator(path,
-              request,
-              ACCEPT_ALL,
-              new Listing.AcceptAllButSelfAndS3nDirs(path));
-      result = new ArrayList<>(files.getBatchSize());
-      while (files.hasNext()) {
-        result.add(files.next());
-      }
-      // merge the results. This will update the store as needed
-      return S3Guard.dirListingUnion(metadataStore, path, result, dirMeta,
-          allowAuthoritative, ttlTimeProvider);
-    } else {
-      LOG.debug("Adding: rd (not a dir): {}", path);
-      S3AFileStatus[] stats = new S3AFileStatus[1];
-      stats[0]= fileStatus;
-      return stats;
     }
+    // Here we have a directory which may or may not be empty.
+    // So we update the metastore and return.
+    return S3Guard.dirListingUnion(
+            metadataStore,
+            path,
+            statusesAssumingNonEmptyDir.getLeft(),
+            statusesAssumingNonEmptyDir.getMiddle(),
+            allowAuthoritative(path),
+            ttlTimeProvider, p ->
+                    listing.createProvidedFileStatusIterator(
+                    dirMetaToStatuses(statusesAssumingNonEmptyDir.getMiddle()),
+                    ACCEPT_ALL,
+                    Listing.ACCEPT_ALL_BUT_S3N));
   }
 
   /**
@@ -4497,7 +4502,7 @@ private RemoteIterator<S3ALocatedFileStatus> getLocatedFileStatusIteratorForDir(
             : null;
     final RemoteIterator<S3AFileStatus> cachedFileStatusIterator =
         listing.createProvidedFileStatusIterator(
-            S3Guard.dirMetaToStatuses(meta), filter, acceptor);
+            dirMetaToStatuses(meta), filter, acceptor);
     return (allowAuthoritative && meta != null
         && meta.isAuthoritative())
         ? listing.createLocatedFileStatusIterator(

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AUtils.java

@@ -42,6 +42,7 @@
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.LocatedFileStatus;
 import org.apache.hadoop.fs.Path;
@@ -1416,6 +1417,30 @@ private static void initUserAgent(Configuration conf,
     awsConf.setUserAgentPrefix(userAgent);
   }
 
+  /**
+   * Convert the data of an iterator of {@link S3AFileStatus} to
+   * an array. Given tombstones are filtered out. If the iterator
+   * does return any item, an empty array is returned.
+   * @param iterator a non-null iterator
+   * @param tombstones
+   * @return a possibly-empty array of file status entries
+   * @throws IOException
+   */
+  public static S3AFileStatus[] iteratorToStatuses(
+      RemoteIterator<S3AFileStatus> iterator, Set<Path> tombstones)
+      throws IOException {
+    List<FileStatus> statuses = new ArrayList<>();
+
+    while (iterator.hasNext()) {
+      S3AFileStatus status = iterator.next();
+      if (!tombstones.contains(status.getPath())) {
+        statuses.add(status);
+      }
+    }
+
+    return statuses.toArray(new S3AFileStatus[0]);
+  }
+
   /**
    * An interface for use in lambda-expressions working with
    * directory tree listings.

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/s3guard/S3Guard.java

@@ -295,30 +295,6 @@ public static BulkOperationState initiateBulkWrite(
     }
   }
 
-  /**
-   * Convert the data of an iterator of {@link S3AFileStatus} to
-   * an array. Given tombstones are filtered out. If the iterator
-   * does return any item, an empty array is returned.
-   * @param iterator a non-null iterator
-   * @param tombstones
-   * @return a possibly-empty array of file status entries
-   * @throws IOException
-   */
-  public static S3AFileStatus[] iteratorToStatuses(
-      RemoteIterator<S3AFileStatus> iterator, Set<Path> tombstones)
-      throws IOException {
-    List<FileStatus> statuses = new ArrayList<>();
-
-    while (iterator.hasNext()) {
-      S3AFileStatus status = iterator.next();
-      if (!tombstones.contains(status.getPath())) {
-        statuses.add(status);
-      }
-    }
-
-    return statuses.toArray(new S3AFileStatus[0]);
-  }
-
   /**
    * Convert the data of a directory listing to an array of {@link FileStatus}
    * entries. Tombstones are filtered out at this point. If the listing is null
@@ -359,17 +335,22 @@ public static S3AFileStatus[] dirMetaToStatuses(DirListingMetadata dirMeta)  {
    * @param dirMeta  Directory listing from MetadataStore.  May be null.
    * @param isAuthoritative State of authoritative mode
    * @param timeProvider Time provider to use when updating entries
+   * @param toStatusItr function to convert array of file status to
+   *                    RemoteIterator.
    * @return Final result of directory listing.
    * @throws IOException if metadata store update failed
    */
-  public static S3AFileStatus[] dirListingUnion(MetadataStore ms, Path path,
-      List<S3AFileStatus> backingStatuses, DirListingMetadata dirMeta,
-      boolean isAuthoritative, ITtlTimeProvider timeProvider)
-      throws IOException {
+  public static RemoteIterator<S3AFileStatus> dirListingUnion(
+          MetadataStore ms, Path path,
+          RemoteIterator<S3AFileStatus> backingStatuses,
+          DirListingMetadata dirMeta, boolean isAuthoritative,
+          ITtlTimeProvider timeProvider,
+          Function<S3AFileStatus[], RemoteIterator<S3AFileStatus>> toStatusItr)
+          throws IOException {
 
     // Fast-path for NullMetadataStore
     if (isNullMetadataStore(ms)) {
-      return backingStatuses.toArray(new S3AFileStatus[backingStatuses.size()]);
+      return backingStatuses;
     }
 
     assertQualified(path);
@@ -410,7 +391,7 @@ public static S3AFileStatus[] dirListingUnion(MetadataStore ms, Path path,
     }
     IOUtils.cleanupWithLogger(LOG, operationState);
 
-    return dirMetaToStatuses(dirMeta);
+    return toStatusItr.apply(dirMetaToStatuses(dirMeta));
   }
 
   /**
@@ -429,7 +410,7 @@ public static S3AFileStatus[] dirListingUnion(MetadataStore ms, Path path,
   private static void authoritativeUnion(
       final MetadataStore ms,
       final Path path,
-      final List<S3AFileStatus> backingStatuses,
+      final RemoteIterator<S3AFileStatus> backingStatuses,
       final DirListingMetadata dirMeta,
       final ITtlTimeProvider timeProvider,
       final BulkOperationState operationState) throws IOException {
@@ -440,7 +421,8 @@ private static void authoritativeUnion(
     Set<Path> deleted = dirMeta.listTombstones();
     final Map<Path, PathMetadata> dirMetaMap = dirMeta.getListing().stream()
         .collect(Collectors.toMap(pm -> pm.getFileStatus().getPath(), pm -> pm));
-    for (S3AFileStatus s : backingStatuses) {
+    while (backingStatuses.hasNext()) {
+      S3AFileStatus s = backingStatuses.next();
       final Path statusPath = s.getPath();
       if (deleted.contains(statusPath)) {
         continue;
@@ -493,16 +475,17 @@ private static void authoritativeUnion(
   private static void nonAuthoritativeUnion(
       final MetadataStore ms,
       final Path path,
-      final List<S3AFileStatus> backingStatuses,
+      final RemoteIterator<S3AFileStatus> backingStatuses,
       final DirListingMetadata dirMeta,
       final ITtlTimeProvider timeProvider,
       final BulkOperationState operationState) throws IOException {
-    List<PathMetadata> entriesToAdd = new ArrayList<>(backingStatuses.size());
+    List<PathMetadata> entriesToAdd = new ArrayList<>();
     Set<Path> deleted = dirMeta.listTombstones();
 
     final Map<Path, PathMetadata> dirMetaMap = dirMeta.getListing().stream()
         .collect(Collectors.toMap(pm -> pm.getFileStatus().getPath(), pm -> pm));
-    for (S3AFileStatus s : backingStatuses) {
+    while (backingStatuses.hasNext()) {
+      S3AFileStatus s = backingStatuses.next();
       final Path statusPath = s.getPath();
       if (deleted.contains(statusPath)) {
         continue;