[GitHub] [iceberg] rdsr commented on a change in pull request #1245: Refactor RemoveSnapshots for easier extension

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

rdsr commented on a change in pull request #1245:
URL: https://github.com/apache/iceberg/pull/1245#discussion_r464047469



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File path: core/src/main/java/org/apache/iceberg/util/ExpireSnapshotUtil.java
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@@ -0,0 +1,394 @@
+/*
+ * 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.util;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+import org.apache.iceberg.GenericManifestFile;
+import org.apache.iceberg.ManifestFile;
+import org.apache.iceberg.Schema;
+import org.apache.iceberg.Snapshot;
+import org.apache.iceberg.SnapshotSummary;
+import org.apache.iceberg.TableMetadata;
+import org.apache.iceberg.avro.Avro;
+import org.apache.iceberg.io.CloseableIterable;
+import org.apache.iceberg.io.FileIO;
+import org.apache.iceberg.relocated.com.google.common.collect.Sets;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+public class ExpireSnapshotUtil {
+  private static final Logger LOG = LoggerFactory.getLogger(ExpireSnapshotUtil.class);
+
+  //Utility Class No Instantiation Allowed
+  private ExpireSnapshotUtil() {}
+
+  /**
+   * Determines the manifest files which need to be inspected because they refer to data files which
+   * can be removed after a Snapshot Expiration.
+   *
+   * Our goal is to determine which manifest files we actually need to read through because they
+   * may refer to files which are no longer accessible from any valid snapshot and do not effect
+   * the current table.
+   *
+   * For this we need to look through
+   *   1. Snapshots which have not expired but contain manifests from expired snapshots
+   *   2. Snapshots which have expired and contain manifests referring to now orphaned files
+   *
+   * @param snapshotChanges       Information about which Snapshots are still valid and which have been expired
+   * @param original              The table metadata from before the snapshot expiration
+   * @param io                    FileIO for reading manifest info
+   * @return Wrapper around which manifests contain references to possibly abandoned files
+   */
+  public static ManifestExpirationChanges determineManifestChangesFromSnapshotExpiration(
+      SnapshotExpirationChanges snapshotChanges, TableMetadata original, FileIO io) {
+
+    AncestorInfo ancestorInfo = getAncestorInfo(original);
+
+    Set<Snapshot> currentSnapshots = snapshotChanges.getValidSnapshots();
+    Set<Snapshot> expiredSnapshots = snapshotChanges.getExpiredSnapshots();
+    Set<Long> validIds = snapshotChanges.getValidSnapshotIds();
+    Set<Long> expiredIds = snapshotChanges.getExpiredSnapshotIds();
+    Set<Long> ancestorIds = ancestorInfo.getAncestorIds();
+
+    //Snapshots which are not expired but refer to manifests from expired snapshots
+    Set<ManifestFile> validManifests = getValidManifests(currentSnapshots, io);
+    Set<ManifestFile> manifestsToScan = findValidManifestsInExpiredSnapshots(validManifests, ancestorInfo, validIds);
+
+    //Snapshots which are expired and do not effect the current table
+    List<Snapshot> snapshotsNotInTableState = findSnapshotsNotInTableState(expiredSnapshots, ancestorInfo);
+    ManifestExpirationChanges manifestExpirationChanges =
+        findExpiredManifestsInUnusedSnapshots(snapshotsNotInTableState, validManifests, ancestorIds, expiredIds, io);
+
+    manifestExpirationChanges.manifestsToScan().addAll(manifestsToScan);
+    return manifestExpirationChanges;
+  }
+
+  /**
+   * Compares the Snapshots from the two TableMetadata objects and identifies the snapshots
+   * still in use and those no longer in use
+   * @param current Metadata from a table after an expiration of snapshots
+   * @param original Metadata from the table before expiration of snapshots
+   * @return Information about which Snapshots have Expired and which are Still Valid
+   */
+  public static SnapshotExpirationChanges getExpiredSnapshots(TableMetadata current, TableMetadata original) {
+
+    Set<Snapshot> validSnapshots = Sets.newHashSet();
+    for (Snapshot snapshot : current.snapshots()) {
+      validSnapshots.add(snapshot);
+    }
+
+    Set<Snapshot> expiredSnapshots = Sets.newHashSet();
+    for (Snapshot snapshot : original.snapshots()) {
+      if (!validSnapshots.contains(snapshot)) {

Review comment:
       Seems like we don't implement `hashcode` and `equals` for `BaseSnapshot`.  Won't that be a problem here?




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