[GitHub] [iceberg] jerryshao commented on a change in pull request #796: Support Spark Structured Streaming Read for Iceberg

[GitBox <gi...@apache.org>]

jerryshao commented on a change in pull request #796:
URL: https://github.com/apache/iceberg/pull/796#discussion_r448975736



##########
File path: core/src/main/java/org/apache/iceberg/Snapshots.java
##########
@@ -0,0 +1,226 @@
+/*
+ * 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.iceberg;
+
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+import org.apache.iceberg.expressions.Expression;
+import org.apache.iceberg.expressions.Expressions;
+import org.apache.iceberg.io.CloseableIterable;
+import org.apache.iceberg.io.FileIO;
+import org.apache.iceberg.relocated.com.google.common.collect.ImmutableList;
+import org.apache.iceberg.relocated.com.google.common.collect.Iterables;
+import org.apache.iceberg.relocated.com.google.common.collect.Lists;
+import org.apache.iceberg.util.Pair;
+
+public class Snapshots {
+  private Snapshots() {
+  }
+
+  public static MicroBatchBuilder from(Snapshot snapshot, FileIO io) {
+    return new MicroBatchBuilder(snapshot, io);
+  }
+
+  public static class MicroBatch {
+    private final long snapshotId;
+    private final int startFileIndex;
+    private final int endFileIndex;
+    private final long sizeInBytes;
+    private final CloseableIterable<FileScanTask> tasks;
+    private final boolean lastIndexOfSnapshot;
+
+    private MicroBatch(long snapshotId, int startFileIndex, int endFileIndex, long sizeInBytes,
+               CloseableIterable<FileScanTask> tasks, boolean lastIndexOfSnapshot) {
+      this.snapshotId = snapshotId;
+      this.startFileIndex = startFileIndex;
+      this.endFileIndex = endFileIndex;
+      this.sizeInBytes = sizeInBytes;
+      this.tasks = tasks;
+      this.lastIndexOfSnapshot = lastIndexOfSnapshot;
+    }
+
+    public long snapshotId() {
+      return snapshotId;
+    }
+
+    public int startFileIndex() {
+      return startFileIndex;
+    }
+
+    public int endFileIndex() {
+      return endFileIndex;
+    }
+
+    public long sizeInBytes() {
+      return sizeInBytes;
+    }
+
+    public CloseableIterable<FileScanTask> tasks() {
+      return tasks;
+    }
+
+    public boolean lastIndexOfSnapshot() {
+      return lastIndexOfSnapshot;
+    }
+  }
+
+  public static class MicroBatchBuilder {
+    private final Snapshot snapshot;
+    private final FileIO io;
+    private Expression rowFilter;
+    private boolean caseSensitive;
+    private Map<Integer, PartitionSpec> specsById;
+
+    private MicroBatchBuilder(Snapshot snapshot, FileIO io) {
+      this.snapshot = snapshot;
+      this.io = io;
+      this.rowFilter = Expressions.alwaysTrue();
+      this.caseSensitive = true;
+    }
+
+    public MicroBatchBuilder caseSensitive(boolean sensitive) {
+      this.caseSensitive = sensitive;
+      return this;
+    }
+
+    public MicroBatchBuilder filter(Expression newRowFilter) {
+      this.rowFilter = newRowFilter;
+      return this;
+    }
+
+    public MicroBatchBuilder specsById(Map<Integer, PartitionSpec> specs) {
+      this.specsById = specs;
+      return this;
+    }
+
+    public MicroBatch generate(int startFileIndex, long targetSizeInBytes, boolean isStarting) {
+      List<ManifestFile> manifests = isStarting ? snapshot.dataManifests() :
+          snapshot.dataManifests().stream().filter(m -> m.snapshotId().equals(snapshot.snapshotId()))
+              .collect(Collectors.toList());
+
+      List<Pair<ManifestFile, Integer>> manifestIndexes = indexManifests(manifests);
+      List<Pair<ManifestFile, Integer>> skippedManifestIndexes = skipManifests(manifestIndexes, startFileIndex);
+
+      return generateMicroBatch(skippedManifestIndexes, startFileIndex, targetSizeInBytes, isStarting);
+    }
+
+    private List<Pair<ManifestFile, Integer>> indexManifests(List<ManifestFile> manifestFiles) {
+      int currentFileIndex = 0;
+      List<Pair<ManifestFile, Integer>> manifestIndexes = Lists.newArrayList();
+
+      for (ManifestFile manifest : manifestFiles) {
+        int filesCount = manifest.addedFilesCount() + manifest.existingFilesCount();
+        manifestIndexes.add(Pair.of(manifest, currentFileIndex));
+        currentFileIndex += filesCount;
+      }
+
+      return manifestIndexes;
+    }
+
+    private List<Pair<ManifestFile, Integer>> skipManifests(List<Pair<ManifestFile, Integer>> indexedManifests,
+                                                            int startFileIndex) {
+      if (startFileIndex == 0) {
+        return indexedManifests;
+      }
+
+      int index = 0;
+      for (Pair<ManifestFile, Integer> manifest : indexedManifests) {
+        if (manifest.second() > startFileIndex) {
+          break;
+        }
+
+        index++;
+      }
+
+      return indexedManifests.subList(index - 1, indexedManifests.size());
+    }
+
+    private MicroBatch generateMicroBatch(List<Pair<ManifestFile, Integer>> indexedManifests,
+                                          int startFileIndex, long targetSizeInBytes, boolean isStarting) {
+      if (indexedManifests.isEmpty()) {
+        return new MicroBatch(snapshot.snapshotId(), startFileIndex, startFileIndex + 1, 0L,
+            CloseableIterable.empty(), true);
+      }
+
+      long currentSizeInBytes = 0L;
+      int currentFileIndex = 0;
+      List<CloseableIterable<FileScanTask>> batchTasks = Lists.newArrayList();
+
+      for (Pair<ManifestFile, Integer> pair : indexedManifests) {
+        currentFileIndex = pair.second();

Review comment:
       Yes @rdblue , if the filter is changed, the offset stored previously cannot be used again, otherwise it will have a possibility of data loss. I was aware of this issue, but it may not be a big problem for streaming applications, since they're typically long-running and will not change during the runtime.
   
   @aokolnychyi 's proposal above doesn't honor filters, so his proposal doesn't have this problem. But ignoring filters also means to read whole data each time, that would also increase the processing overhead.




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