[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_r512401360



##########
File path: spark2/src/main/java/org/apache/iceberg/spark/source/StreamingReader.java
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@@ -0,0 +1,323 @@
+/*
+ * 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 java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collectors;
+import org.apache.iceberg.CombinedScanTask;
+import org.apache.iceberg.DataOperations;
+import org.apache.iceberg.FileScanTask;
+import org.apache.iceberg.MicroBatches;
+import org.apache.iceberg.MicroBatches.MicroBatch;
+import org.apache.iceberg.Snapshot;
+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.relocated.com.google.common.annotations.VisibleForTesting;
+import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
+import org.apache.iceberg.relocated.com.google.common.collect.ImmutableList;
+import org.apache.iceberg.relocated.com.google.common.collect.Lists;
+import org.apache.iceberg.util.Pair;
+import org.apache.iceberg.util.PropertyUtil;
+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;
+
+import static org.apache.iceberg.TableProperties.SPLIT_LOOKBACK;
+import static org.apache.iceberg.TableProperties.SPLIT_LOOKBACK_DEFAULT;
+import static org.apache.iceberg.TableProperties.SPLIT_OPEN_FILE_COST;
+import static org.apache.iceberg.TableProperties.SPLIT_OPEN_FILE_COST_DEFAULT;
+import static org.apache.iceberg.TableProperties.SPLIT_SIZE;
+import static org.apache.iceberg.TableProperties.SPLIT_SIZE_DEFAULT;
+
+/**
+ * A micro-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 StreamingOffset startOffset;
+  private StreamingOffset endOffset;
+
+  private final Table table;
+  private final long maxSizePerBatch;
+  private final Long startSnapshotId;
+  private final long splitSize;
+  private final int splitLookback;
+  private final long splitOpenFileCost;
+  private Boolean readUsingBatch = null;
+
+  // Used to cache the pending batches for this streaming batch interval.
+  private Pair<StreamingOffset, List<MicroBatch>> cachedPendingBatches = null;
+
+  StreamingReader(Table table, Broadcast<FileIO> io, Broadcast<EncryptionManager> encryptionManager,
+                  boolean caseSensitive, DataSourceOptions options) {
+    super(table, io, encryptionManager, caseSensitive, options);
+
+    this.table = table;
+    this.maxSizePerBatch = options.get("max-size-per-batch").map(Long::parseLong).orElse(Long.MAX_VALUE);
+    Preconditions.checkArgument(maxSizePerBatch > 0L,
+        "Option max-size-per-batch '%s' should > 0", maxSizePerBatch);
+
+    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");
+      }
+    }
+
+    this.splitSize = Optional.ofNullable(splitSize())
+        .orElseGet(() -> PropertyUtil.propertyAsLong(table.properties(), SPLIT_SIZE, SPLIT_SIZE_DEFAULT));
+    this.splitLookback = Optional.ofNullable(splitLookback())
+        .orElseGet(() -> PropertyUtil.propertyAsInt(table.properties(), SPLIT_LOOKBACK, SPLIT_LOOKBACK_DEFAULT));
+    this.splitOpenFileCost = Optional.ofNullable(splitOpenFileCost())
+        .orElseGet(() ->
+            PropertyUtil.propertyAsLong(table.properties(), SPLIT_OPEN_FILE_COST, SPLIT_OPEN_FILE_COST_DEFAULT));
+  }
+
+  @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.orElseGet(() -> 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
+  public boolean enableBatchRead() {
+    return readUsingBatch == null ? false : readUsingBatch;
+  }
+
+  @Override
+  public String toString() {
+    return String.format(
+        "IcebergStreamScan(table=%s, type=%s)", table, table.schema().asStruct());
+  }
+
+  @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(cachedPendingBatches != null,
+        "pendingBatches is null, which is unexpected as it will be set when calculating end offset");

Review comment:
       This is to check and fail the unexpected scenario, normally `cachedPendingBatches` should not be null.




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