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

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aokolnychyi commented on a change in pull request #796: Support Spark Structured Streaming Read for Iceberg
URL: https://github.com/apache/incubator-iceberg/pull/796#discussion_r407100148
 
 

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 File path: spark/src/main/java/org/apache/iceberg/spark/source/StreamingReader.java
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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.iceberg.spark.source;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Iterables;
+import com.google.common.collect.Lists;
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import org.apache.commons.lang3.tuple.Pair;
+import org.apache.iceberg.CombinedScanTask;
+import org.apache.iceberg.FileScanTask;
+import org.apache.iceberg.Table;
+import org.apache.iceberg.encryption.EncryptionManager;
+import org.apache.iceberg.io.CloseableIterable;
+import org.apache.iceberg.io.FileIO;
+import org.apache.iceberg.util.SnapshotUtil;
+import org.apache.iceberg.util.TableScanUtil;
+import org.apache.spark.broadcast.Broadcast;
+import org.apache.spark.sql.sources.v2.DataSourceOptions;
+import org.apache.spark.sql.sources.v2.reader.streaming.MicroBatchReader;
+import org.apache.spark.sql.sources.v2.reader.streaming.Offset;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A mirco-batch based Spark Structured Streaming reader for Iceberg table. It will track the added
+ * files and generate tasks per batch to process newly added files. By default it will process
+ * all the newly added files to the current snapshot in each batch, user could also set this
+ * configuration "max-files-per-trigger" to control the number of files processed per batch.
+ */
+class StreamingReader extends Reader implements MicroBatchReader {
+  private static final Logger LOG = LoggerFactory.getLogger(StreamingReader.class);
+  private static final int DEFAULT_MAX_FILES_PER_BATCH = 1000;
+
+  private StreamingOffset startOffset;
+  private StreamingOffset endOffset;
+
+  private final Table table;
+  private final int maxFilesPerBatch;
+  private final Long startSnapshotId;
+
+  // Used to cache the pending tasks of this batch
+  private CloseableIterable<IndexedTask> pendingTasks;
+
+  /**
+   * Utility class to track the snapshotId, task and index of task within this snapshot.
+   */
+  @VisibleForTesting
+  static class IndexedTask {
+    private final long snapshotId;
+    private final FileScanTask task;
+    private final int index;
+
+    IndexedTask(long snapshotId, FileScanTask task, int index) {
+      this.snapshotId = snapshotId;
+      this.task = task;
+      this.index = index;
+    }
+
+    long snapshotId() {
+      return snapshotId;
+    }
+
+    FileScanTask task() {
+      return task;
+    }
+
+    int index() {
+      return index;
+    }
+  }
+
+  StreamingReader(Table table, Broadcast<FileIO> io, Broadcast<EncryptionManager> encryptionManager,
+                  boolean caseSensitive, DataSourceOptions options) {
+    super(table, io, encryptionManager, caseSensitive, options);
+
+    this.table = table;
+    this.maxFilesPerBatch =
+       options.get("max-files-per-batch").map(Integer::parseInt).orElse(DEFAULT_MAX_FILES_PER_BATCH);
+    Preconditions.checkArgument(maxFilesPerBatch > 0,
+        "Option max-files-per-batch '%d' should > 0", maxFilesPerBatch);
+
+    this.startSnapshotId = options.get("starting-snapshot-id").map(Long::parseLong).orElse(null);
+    if (startSnapshotId != null) {
+      if (!SnapshotUtil.ancestorOf(table, table.currentSnapshot().snapshotId(), startSnapshotId)) {
+        throw new IllegalStateException("The option starting-snapshot-id " + startSnapshotId +
+            " is not an ancestor of the current snapshot");
+      }
+    }
+  }
+
+  @Override
+  @SuppressWarnings("unchecked")
+  public void setOffsetRange(Optional<Offset> start, Optional<Offset> end) {
+    table.refresh();
+
+    if (start.isPresent() && !StreamingOffset.START_OFFSET.equals(start.get())) {
+      this.startOffset = (StreamingOffset) start.get();
+      this.endOffset = (StreamingOffset) end.orElse(calculateEndOffset(startOffset));
+    } else {
+      // If starting offset is "START_OFFSET" (there's no snapshot in the last batch), or starting
+      // offset is not set, then we need to calculate the starting offset again.
+      this.startOffset = calculateStartingOffset();
+      this.endOffset = calculateEndOffset(startOffset);
+    }
+  }
+
+  @Override
+  public Offset getStartOffset() {
+    if (startOffset == null) {
+      throw new IllegalStateException("Start offset is not set");
+    }
+
+    return startOffset;
+  }
+
+  @Override
+  public Offset getEndOffset() {
+    if (endOffset == null) {
+      throw new IllegalStateException("End offset is not set");
+    }
+
+    return endOffset;
+  }
+
+  @Override
+  public Offset deserializeOffset(String json) {
+    return StreamingOffset.fromJson(json);
+  }
+
+  @Override
+  public void commit(Offset end) {
+    // Since all the data and metadata of Iceberg is as it is, nothing needs to commit when
+    // offset is processed, so no need to implement this method.
+  }
+
+  @Override
+  public void stop() {}
+
+  @Override
+  @SuppressWarnings("unchecked")
+  protected List<CombinedScanTask> tasks() {
+    if (startOffset.equals(endOffset)) {
+      LOG.info("Start offset {} equals to end offset {}, no data to process", startOffset, endOffset);
+      return Collections.emptyList();
+    }
+
+    Preconditions.checkState(pendingTasks != null,
+        "pendingTasks is null, which is unexpected as it will be set when calculating end offset");
+
+    if (Iterables.isEmpty(pendingTasks)) {
+      LOG.info("There's no task to process in this batch");
+      return Collections.emptyList();
+    }
+
+    IndexedTask last = Iterables.getLast(pendingTasks);
+    if (last.snapshotId() != endOffset.snapshotId() || last.index() != endOffset.index()) {
+      throw new IllegalStateException("The cached pendingTasks doesn't match the current end offset " + endOffset);
+    }
+
+    LOG.info("Processing data from {} exclusive to {} inclusive", startOffset, endOffset);
+    CloseableIterable<FileScanTask> splitTasks = TableScanUtil.splitFiles(
+        CloseableIterable.transform(pendingTasks, IndexedTask::task), splitSize());
+    return Lists.newArrayList(
+        TableScanUtil.planTasks(splitTasks, splitSize(), splitLookback(), splitOpenFileCost()));
+  }
+
+  private StreamingOffset calculateStartingOffset() {
 
 Review comment:
   There is one case where this might be important: users can do some preparations on existing tables before starting a stream. In that case, there will be multiple snapshots and some of them can have deletes.

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