nandakumar131 commented on code in PR #3885: URL: https://github.com/apache/ozone/pull/3885#discussion_r1009763752
########## hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/SnapshotDiffManager.java: ########## @@ -0,0 +1,223 @@ +/* + * 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 + * <p> + * http://www.apache.org/licenses/LICENSE-2.0 + * <p> + * 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.hadoop.ozone.om.snapshot; + +import org.apache.hadoop.hdds.utils.db.Table; +import org.apache.hadoop.ozone.om.OMMetadataManager; +import org.apache.hadoop.ozone.om.OmSnapshot; +import org.apache.hadoop.ozone.om.helpers.BucketLayout; +import org.apache.hadoop.ozone.om.helpers.OmKeyInfo; +import org.apache.hadoop.ozone.om.snapshot.SnapshotDiffReport.DiffType; +import org.apache.hadoop.ozone.om.snapshot.SnapshotDiffReport.DiffReportEntry; + +import org.apache.ozone.rocksdb.util.ManagedSSTFileReader; +import org.rocksdb.RocksDBException; + +import java.io.IOException; +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.stream.Stream; + +public class SnapshotDiffManager { + + public SnapshotDiffReport getSnapshotDiffReport(final String volume, + final String bucket, + final OmSnapshot fromSnapshot, + final OmSnapshot toSnapshot) + throws IOException, RocksDBException { + + // TODO: Once RocksDBCheckpointDiffer exposes method to get list + // of delta SST files, plug it in here. + + final Set<String> deltaFiles = Collections.emptySet(); + + // TODO: Filter out the files. + + final Stream<String> keysToCheck = new ManagedSSTFileReader(deltaFiles) + .getKeyStream(); + + final BucketLayout bucketLayout = getBucketLayout(volume, bucket, + fromSnapshot.getMetadataManager()); + + final Table<String, OmKeyInfo> fsKeyTable = fromSnapshot + .getMetadataManager().getKeyTable(bucketLayout); + final Table<String, OmKeyInfo> tsKeyTable = toSnapshot + .getMetadataManager().getKeyTable(bucketLayout); + + /* + * The reason for having ObjectID to KeyName mapping instead of OmKeyInfo + * is to reduce the memory footprint. + */ + final Map<Long, String> oldObjIdToKeyMap = new HashMap<>(); + // Long --> const. length + // String --> var. length "/dir1/dir2/dir3/dir4/dir5/key1" + final Map<Long, String> newObjIdToKeyMap = new HashMap<>(); + + final Set<Long> objectIDsToCheck = new HashSet<>(); + + keysToCheck.forEach(key -> { + try { + final OmKeyInfo oldKey = fsKeyTable.get(key); + final OmKeyInfo newKey = tsKeyTable.get(key); + if (areKeysEqual(oldKey, newKey)) { + // We don't have to do anything. + return; + } + if (oldKey != null) { + final long oldObjId = oldKey.getObjectID(); + oldObjIdToKeyMap.put(oldObjId, oldKey.getKeyName()); + objectIDsToCheck.add(oldObjId); + } + if (newKey != null) { + final long newObjId = newKey.getObjectID(); + newObjIdToKeyMap.put(newObjId, newKey.getKeyName()); + objectIDsToCheck.add(newObjId); + } + } catch (IOException e) { + throw new RuntimeException(e); + } + }); + keysToCheck.close(); + + return new SnapshotDiffReport(volume, bucket, fromSnapshot.getName(), + toSnapshot.getName(), generateDiffReport(objectIDsToCheck, + oldObjIdToKeyMap, newObjIdToKeyMap)); + } + + private List<DiffReportEntry> generateDiffReport( + final Set<Long> objectIDsToCheck, + final Map<Long, String> oldObjIdToKeyMap, + final Map<Long, String> newObjIdToKeyMap) { + + final List<DiffReportEntry> deleteDiffs = new ArrayList<>(); + final List<DiffReportEntry> renameDiffs = new ArrayList<>(); + final List<DiffReportEntry> createDiffs = new ArrayList<>(); + final List<DiffReportEntry> modifyDiffs = new ArrayList<>(); + + + for (Long id : objectIDsToCheck) { + /* + * This key can be + * -> Created after the old snapshot was taken, which means it will be + * missing in oldKeyTable and present in newKeyTable. + * -> Deleted after the old snapshot was taken, which means it will be + * present in oldKeyTable and missing in newKeyTable. + * -> Modified after the old snapshot was taken, which means it will be + * present in oldKeyTable and present in newKeyTable with same + * Object ID but with different metadata. + * -> Renamed after the old snapshot was taken, which means it will be + * present in oldKeyTable and present in newKeyTable but with different + * name and same Object ID. + */ + + final String oldKeyName = oldObjIdToKeyMap.get(id); + final String newKeyName = newObjIdToKeyMap.get(id); + + if (oldKeyName == null && newKeyName == null) { + // This cannot happen. + continue; + } + + // Key Created. + if (oldKeyName == null) { + createDiffs.add(DiffReportEntry.of(DiffType.CREATE, newKeyName)); + continue; + } + + // Key Deleted. + if(newKeyName == null) { + deleteDiffs.add(DiffReportEntry.of(DiffType.DELETE, oldKeyName)); + continue; + } + + // Key modified. + if(oldKeyName.equals(newKeyName)) { + modifyDiffs.add(DiffReportEntry.of(DiffType.MODIFY, newKeyName)); + continue; + } + + // Key Renamed. + renameDiffs.add(DiffReportEntry.of(DiffType.RENAME, + oldKeyName, newKeyName)); + } + /* + * The order in which snap-diff should be applied + * + * 1. Delete diffs + * 2. Rename diffs + * 3. Create diffs + * 4. Modified diffs + * + * Consider the following scenario + * + * 1. File "A" is created. + * 2. File "B" is created. + * 3. File "C" is created. + * Snapshot "1" is taken. + * + * Case 1: + * 1. File "A" is deleted. + * 2. File "B" is renamed to "A". + * Snapshot "2" is taken. + * + * Snapshot diff should be applied in the following order: + * 1. Delete "A" + * 2. Rename "B" to "A" + * + * + * Case 2: + * 1. File "B" is renamed to "C". + * 2. File "B" is created. + * Snapshot "2" is taken. + * + * Snapshot diff should be applied in the following order: + * 1. Rename "B" to "C" + * 2. Create "B" + * + */ + + final List<DiffReportEntry> snapshotDiffs = new ArrayList<>(); + snapshotDiffs.addAll(deleteDiffs); + snapshotDiffs.addAll(renameDiffs); + snapshotDiffs.addAll(createDiffs); + snapshotDiffs.addAll(modifyDiffs); + return snapshotDiffs; + } + + private BucketLayout getBucketLayout(final String volume, + final String bucket, + final OMMetadataManager mManager) + throws IOException { + final String bucketTableKey = mManager.getBucketKey(volume, bucket); + return mManager.getBucketTable().get(bucketTableKey).getBucketLayout(); Review Comment: `mManager.getBucketKey(volume, bucket)` can never return null. `mManager.getBucketTable().get(bucketTableKey)` should not return null once we implement proper locking logic in the snapshot code. For now, it is theoretically possible to get a null pointer exception here. -- This is an automated message from the Apache Git Service. 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