[GitHub] [iceberg] rdblue commented on a diff in pull request #4329: Flink: FLIP-27 source enumerator help classes

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

rdblue commented on code in PR #4329:
URL: https://github.com/apache/iceberg/pull/4329#discussion_r890309210


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flink/v1.14/flink/src/main/java/org/apache/iceberg/flink/source/enumerator/ContinuousSplitPlannerImpl.java:
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@@ -0,0 +1,184 @@
+/*
+ * 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.flink.source.enumerator;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import java.util.concurrent.ExecutorService;
+import org.apache.flink.annotation.Internal;
+import org.apache.flink.annotation.VisibleForTesting;
+import org.apache.flink.util.Preconditions;
+import org.apache.iceberg.Snapshot;
+import org.apache.iceberg.Table;
+import org.apache.iceberg.flink.source.FlinkSplitPlanner;
+import org.apache.iceberg.flink.source.ScanContext;
+import org.apache.iceberg.flink.source.StreamingStartingStrategy;
+import org.apache.iceberg.flink.source.split.IcebergSourceSplit;
+import org.apache.iceberg.util.SnapshotUtil;
+import org.apache.iceberg.util.ThreadPools;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+@Internal
+public class ContinuousSplitPlannerImpl implements ContinuousSplitPlanner {
+  private static final Logger LOG = LoggerFactory.getLogger(ContinuousSplitPlannerImpl.class);
+
+  private final Table table;
+  private final ScanContext scanContext;
+  private final ExecutorService workerPool;
+
+  public ContinuousSplitPlannerImpl(Table table, ScanContext scanContext, String threadPoolName) {
+    this.table = table;
+    this.scanContext = scanContext;
+    this.workerPool = ThreadPools.newWorkerPool(
+        "iceberg-plan-worker-pool-" + threadPoolName, scanContext.planParallelism());
+  }
+
+  @Override
+  public ContinuousEnumerationResult planSplits(IcebergEnumeratorPosition lastPosition) {
+    table.refresh();
+    if (lastPosition != null) {
+      return discoverIncrementalSplits(lastPosition);
+    } else {
+      return discoverInitialSplits();
+    }
+  }
+
+  /**
+   * Discover incremental changes between @{code lastPosition} and current table snapshot
+   */
+  private ContinuousEnumerationResult discoverIncrementalSplits(IcebergEnumeratorPosition lastPosition) {
+    Snapshot currentSnapshot = table.currentSnapshot();
+    if (currentSnapshot == null) {
+      // empty table
+      Preconditions.checkArgument(lastPosition.snapshotId() == null,
+          "Invalid last enumerated position for an empty table: not null");
+      LOG.info("Skip incremental scan because table is empty");
+      return new ContinuousEnumerationResult(Collections.emptyList(), lastPosition, lastPosition);
+    } else {
+      if (lastPosition.snapshotId() != null && currentSnapshot.snapshotId() == lastPosition.snapshotId()) {
+        LOG.info("Current table snapshot is already enumerated: {}", currentSnapshot.snapshotId());
+        return new ContinuousEnumerationResult(Collections.emptyList(), lastPosition, lastPosition);
+      } else {
+        IcebergEnumeratorPosition newPosition = IcebergEnumeratorPosition.of(
+            currentSnapshot.snapshotId(), currentSnapshot.timestampMillis());
+        ScanContext incrementalScan = scanContext
+            .copyWithAppendsBetween(lastPosition.snapshotId(), currentSnapshot.snapshotId());
+        List<IcebergSourceSplit> splits = FlinkSplitPlanner.planIcebergSourceSplits(table, incrementalScan, workerPool);
+        LOG.info("Discovered {} splits from incremental scan: " +
+                "from snapshot (exclusive) is {}, to snapshot (inclusive) is {}",
+            splits.size(), lastPosition, newPosition);
+        return new ContinuousEnumerationResult(splits, lastPosition, newPosition);
+      }
+    }
+  }
+
+  /**
+   * Discovery initial set of splits based on {@link StreamingStartingStrategy}.
+   *
+   * <li>{@link ContinuousEnumerationResult#splits()} should contain initial splits
+   * discovered from table scan for {@link StreamingStartingStrategy#TABLE_SCAN_THEN_INCREMENTAL}.
+   * For all other strategies, splits collection should be empty.
+   * <li>{@link ContinuousEnumerationResult#toPosition()} points to the starting position
+   * for the next incremental split discovery with exclusive behavior. Meaning files committed
+   * by the snapshot from the position in {@code ContinuousEnumerationResult} won't be included
+   * in the next incremental scan.
+   */
+  private ContinuousEnumerationResult discoverInitialSplits() {
+    Optional<Snapshot> startSnapshotOptional = startSnapshot(table, scanContext);
+    if (!startSnapshotOptional.isPresent()) {
+      return new ContinuousEnumerationResult(Collections.emptyList(), null,
+          IcebergEnumeratorPosition.empty());
+    }
+
+    Snapshot startSnapshot = startSnapshotOptional.get();
+    LOG.info("Get starting snapshot id {} based on strategy {}",
+        startSnapshot.snapshotId(), scanContext.startingStrategy());
+    List<IcebergSourceSplit> splits;
+    IcebergEnumeratorPosition toPosition;
+    if (scanContext.startingStrategy() == StreamingStartingStrategy.TABLE_SCAN_THEN_INCREMENTAL) {
+      // do a batch table scan first
+      splits = FlinkSplitPlanner.planIcebergSourceSplits(table, scanContext, workerPool);
+      LOG.info("Discovered {} splits from initial batch table scan with snapshot Id {}",
+          splits.size(), startSnapshot.snapshotId());
+      // For TABLE_SCAN_THEN_INCREMENTAL, incremental mode starts exclusive from the startSnapshot
+      toPosition = IcebergEnumeratorPosition.of(startSnapshot.snapshotId(), startSnapshot.timestampMillis());
+    } else {
+      // For all other modes, starting snapshot should be consumed inclusively.
+      // Use parentId to achieve the inclusive behavior. It is fine if parentId is null.
+      splits = Collections.emptyList();
+      Long parentSnapshotId = startSnapshot.parentId();
+      if (parentSnapshotId != null) {
+        Snapshot parentSnapshot = table.snapshot(parentSnapshotId);
+        Long parentSnapshotTimestampMs = parentSnapshot != null ? parentSnapshot.timestampMillis() : null;
+        toPosition = IcebergEnumeratorPosition.of(parentSnapshotId, parentSnapshotTimestampMs);
+      } else {
+        toPosition = IcebergEnumeratorPosition.empty();
+      }
+
+      LOG.info("Start incremental scan with start snapshot (inclusive): id = {}, timestamp = {}",
+          startSnapshot.snapshotId(), startSnapshot.timestampMillis());
+    }
+
+    return new ContinuousEnumerationResult(splits, null, toPosition);
+  }
+
+  /**
+   * Calculate the starting snapshot based on the {@link StreamingStartingStrategy} defined in {@code ScanContext}.
+   * <p>
+   * If the {@link StreamingStartingStrategy} is not {@link StreamingStartingStrategy#TABLE_SCAN_THEN_INCREMENTAL},
+   * the start snapshot should be consumed inclusively.
+   */
+  @VisibleForTesting
+  static Optional<Snapshot> startSnapshot(Table table, ScanContext scanContext) {
+    switch (scanContext.startingStrategy()) {
+      case TABLE_SCAN_THEN_INCREMENTAL:
+      case INCREMENTAL_FROM_LATEST_SNAPSHOT:
+        return Optional.ofNullable(table.currentSnapshot());
+      case INCREMENTAL_FROM_EARLIEST_SNAPSHOT:
+        return Optional.ofNullable(SnapshotUtil.oldestAncestor(table));
+      case INCREMENTAL_FROM_SNAPSHOT_ID:
+        Snapshot matchedSnapshotById = table.snapshot(scanContext.startSnapshotId());
+        if (matchedSnapshotById != null) {
+          return Optional.of(matchedSnapshotById);
+        } else {
+          throw new IllegalArgumentException(

Review Comment:
   We usually prefer `Preconditions.checkArgument` instead of an extra `if` statement.



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