jojochuang commented on code in PR #9324:
URL: https://github.com/apache/ozone/pull/9324#discussion_r2557326373


##########
hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/defrag/SnapshotDefragService.java:
##########
@@ -135,48 +196,322 @@ private boolean isRocksToolsNativeLibAvailable() {
   }
 
   /**
-   * Checks if a snapshot needs defragmentation by examining its YAML metadata.
+   * Determines whether the specified snapshot requires defragmentation and 
returns
+   * a pair indicating the need for defragmentation and the corresponding 
version of the snapshot.
+   *
+   * @param snapshotInfo Information about the snapshot to be checked for 
defragmentation.
+   * @return A pair containing a boolean value and an integer:
+   *         - The boolean value indicates whether the snapshot requires 
defragmentation
+   *         (true if needed, false otherwise).
+   *         - The integer represents the version of the snapshot being 
evaluated.
+   * @throws IOException If an I/O error occurs while accessing the local 
snapshot data or metadata.
    */
-  private boolean needsDefragmentation(SnapshotInfo snapshotInfo) {
-    if (!SstFilteringService.isSstFiltered(conf, snapshotInfo)) {
-      return false;
-    }
-    try (OmSnapshotLocalDataManager.ReadableOmSnapshotLocalDataProvider 
readableOmSnapshotLocalDataProvider =
-             
ozoneManager.getOmSnapshotManager().getSnapshotLocalDataManager().getOmSnapshotLocalData(snapshotInfo))
 {
-      Path snapshotPath = OmSnapshotManager.getSnapshotPath(
-          ozoneManager.getMetadataManager(), snapshotInfo,
-          
readableOmSnapshotLocalDataProvider.getSnapshotLocalData().getVersion());
+  private Pair<Boolean, Integer> needsDefragmentation(SnapshotInfo 
snapshotInfo) throws IOException {
+    // Update snapshot local metadata to point to the correct previous 
snapshotId if it was different and check if
+    // snapshot needs defrag.
+    try (WritableOmSnapshotLocalDataProvider 
writableOmSnapshotLocalDataProvider =
+             
snapshotLocalDataManager.getWritableOmSnapshotLocalData(snapshotInfo)) {
       // Read snapshot local metadata from YAML
       // Check if snapshot needs compaction (defragmentation)
-      boolean needsDefrag = readableOmSnapshotLocalDataProvider.needsDefrag();
-      LOG.debug("Snapshot {} needsDefragmentation field value: {}", 
snapshotInfo.getName(), needsDefrag);
+      writableOmSnapshotLocalDataProvider.commit();
+      boolean needsDefrag = writableOmSnapshotLocalDataProvider.needsDefrag();
+      OmSnapshotLocalData localData = 
writableOmSnapshotLocalDataProvider.getSnapshotLocalData();
+      if (!needsDefrag) {
+        OmSnapshotLocalData previousLocalData = 
writableOmSnapshotLocalDataProvider.getPreviousSnapshotLocalData();
+        LOG.debug("Skipping defragmentation since snapshot has already been 
defragmented: id : {}(version: {}=>{}) " +
+                "previousId: {}(version: {})", snapshotInfo.getSnapshotId(), 
localData.getVersion(),
+            
localData.getVersionSstFileInfos().get(localData.getVersion()).getPreviousSnapshotVersion(),
+            snapshotInfo.getPathPreviousSnapshotId(), 
previousLocalData.getVersion());
+      } else {
+        LOG.debug("Snapshot {} needsDefragmentation field value: true", 
snapshotInfo.getSnapshotId());
+      }
+      return Pair.of(needsDefrag, localData.getVersion());
+    }
+  }
 
-      return needsDefrag;
-    } catch (IOException e) {
-      LOG.warn("Failed to read YAML metadata for snapshot {}, assuming defrag 
needed",
-          snapshotInfo.getName(), e);
-      return true;
+  private Pair<String, String> getTableBounds(Table<String, ?> table) throws 
RocksDatabaseException, CodecException {
+    String tableLowestValue = null, tableHighestValue = null;
+    try (TableIterator<String, String> keyIterator = table.keyIterator()) {
+      if (keyIterator.hasNext()) {
+        // Setting the lowest value to the first key in the table.
+        tableLowestValue = keyIterator.next();
+      }
+      keyIterator.seekToLast();
+      if (keyIterator.hasNext()) {
+        // Setting the highest value to the last key in the table.
+        tableHighestValue = keyIterator.next();
+      }
     }
+    return Pair.of(tableLowestValue, tableHighestValue);
   }
 
   /**
-   * Performs full defragmentation for the first snapshot in the chain.
-   * This is a simplified implementation that demonstrates the concept.
+   * Performs a full defragmentation process for specified tables in the 
metadata manager.
+   * This method processes all the entries in the tables for the provided 
prefix information,
+   * deletes specified key ranges, and compacts the tables to remove 
tombstones.
+   *
+   * @param checkpointDBStore the metadata manager responsible for managing 
tables during the checkpoint process
+   * @param prefixInfo the prefix information used to identify bucket prefix 
and determine key ranges in the tables
+   * @param incrementalTables the set of tables for which incremental 
defragmentation is performed.
+   * @throws IOException if an I/O error occurs during table operations or 
compaction
    */
-  private void performFullDefragmentation(SnapshotInfo snapshotInfo,
-      OmSnapshot omSnapshot) throws IOException {
-
-    // TODO: Implement full defragmentation
+  private void performFullDefragmentation(DBStore checkpointDBStore, 
TablePrefixInfo prefixInfo,
+      Set<String> incrementalTables) throws IOException {
+    for (String table : incrementalTables) {
+      Table<String, byte[]> checkpointTable = 
checkpointDBStore.getTable(table, StringCodec.get(),
+          ByteArrayCodec.get());
+      String tableBucketPrefix = prefixInfo.getTablePrefix(table);
+      String prefixUpperBound = 
getLexicographicallyHigherString(tableBucketPrefix);
+
+      Pair<String, String> tableBounds = getTableBounds(checkpointTable);
+      String tableLowestValue = tableBounds.getLeft();
+      String tableHighestValue = tableBounds.getRight();
+
+      // If lowest value is not null and if the bucket prefix corresponding to 
the table is greater than lower then
+      // delete the range between lowest value and bucket prefix.
+      if (tableLowestValue != null && 
tableLowestValue.compareTo(tableBucketPrefix) < 0) {
+        checkpointTable.deleteRange(tableLowestValue, tableBucketPrefix);
+      }
+      // If highest value is not null and if the next higher lexicographical 
string of bucket prefix corresponding to
+      // the table is less than equal to the highest value then delete the 
range between bucket prefix
+      // and also the highest value.
+      if (tableHighestValue != null && 
tableHighestValue.compareTo(prefixUpperBound) >= 0) {
+        checkpointTable.deleteRange(tableBucketPrefix, tableHighestValue);
+        checkpointTable.delete(tableHighestValue);
+      }
+      // Compact the table completely with kForce to get rid of tombstones.
+      try (ManagedCompactRangeOptions compactRangeOptions = new 
ManagedCompactRangeOptions()) {
+        
compactRangeOptions.setBottommostLevelCompaction(ManagedCompactRangeOptions.BottommostLevelCompaction.kForce);
+        compactRangeOptions.setExclusiveManualCompaction(true);
+        checkpointDBStore.compactTable(table, compactRangeOptions);
+      }
+    }
   }
 
   /**
-   * Performs incremental defragmentation using diff from previous 
defragmented snapshot.
+   * Performs an incremental defragmentation process, which involves 
determining
+   * and processing delta files between snapshots for metadata updates. The 
method
+   * computes the changes, manages file ingestion to the checkpoint metadata 
manager,
+   * and ensures that all delta files are deleted after processing.
+   *
+   * @param previousSnapshotInfo information about the previous snapshot.
+   * @param snapshotInfo information about the current snapshot for which
+   *                     incremental defragmentation is performed.
+   * @param snapshotVersion the version of the snapshot to be processed.
+   * @param checkpointStore the dbStore instance where data
+   *                        updates are ingested after being processed.
+   * @param bucketPrefixInfo table prefix information associated with buckets,
+   *                         used to determine bounds for processing keys.
+   * @param incrementalTables the set of tables for which incremental 
defragmentation is performed.
+   * @throws IOException if an I/O error occurs during processing.
    */
-  private void performIncrementalDefragmentation(SnapshotInfo currentSnapshot,
-      SnapshotInfo previousDefraggedSnapshot, OmSnapshot currentOmSnapshot)
+  private void performIncrementalDefragmentation(SnapshotInfo 
previousSnapshotInfo, SnapshotInfo snapshotInfo,
+      int snapshotVersion, DBStore checkpointStore, TablePrefixInfo 
bucketPrefixInfo, Set<String> incrementalTables)
       throws IOException {
+    // Map of delta files grouped on the basis of the tableName.
+    Collection<Pair<Path, SstFileInfo>> allTableDeltaFiles = 
this.deltaDiffComputer.getDeltaFiles(
+        previousSnapshotInfo, snapshotInfo, incrementalTables);
+
+    Map<String, List<Pair<Path, SstFileInfo>>> tableGroupedDeltaFiles = 
allTableDeltaFiles.stream()
+        .collect(Collectors.groupingBy(pair -> 
pair.getValue().getColumnFamily()));
+
+    String volumeName = snapshotInfo.getVolumeName();
+    String bucketName = snapshotInfo.getBucketName();
+
+    Set<Path> filesToBeDeleted = new HashSet<>();
+    // All files computed as delta must be deleted irrespective of whether 
ingestion succeeded or not.
+    allTableDeltaFiles.forEach(pair -> filesToBeDeleted.add(pair.getKey()));
+    try (UncheckedAutoCloseableSupplier<OmSnapshot> snapshot = 
omSnapshotManager.getActiveSnapshot(volumeName,
+        bucketName, snapshotInfo.getName());
+         UncheckedAutoCloseableSupplier<OmSnapshot> previousSnapshot = 
omSnapshotManager.getActiveSnapshot(
+             volumeName, bucketName, previousSnapshotInfo.getName())) {
+      for (Map.Entry<String, List<Pair<Path, SstFileInfo>>> entry : 
tableGroupedDeltaFiles.entrySet()) {
+        String table = entry.getKey();
+        List<Pair<Path, SstFileInfo>> deltaFiles = entry.getValue();
+        Path fileToBeIngested;
+        if (deltaFiles.size() == 1 && snapshotVersion > 0) {
+          // If there is only one delta file for the table and the snapshot 
version is also not 0 then the same delta
+          // file can reingested into the checkpointStore.
+          fileToBeIngested = deltaFiles.get(0).getKey();
+        } else {
+          Table<String, byte[]> snapshotTable = 
snapshot.get().getMetadataManager().getStore()
+              .getTable(table, StringCodec.get(), ByteArrayCodec.get());
+          Table<String, byte[]> previousSnapshotTable = 
previousSnapshot.get().getMetadataManager().getStore()
+              .getTable(table, StringCodec.get(), ByteArrayCodec.get());
+
+          String tableBucketPrefix = bucketPrefixInfo.getTablePrefix(table);
+          String sstFileReaderLowerBound = 
bucketPrefixInfo.getTablePrefix(entry.getKey());
+          String sstFileReaderUpperBound = null;
+          if (Strings.isNotEmpty(sstFileReaderLowerBound)) {
+            sstFileReaderUpperBound = 
getLexicographicallyHigherString(sstFileReaderLowerBound);
+          }
+          List<Path> deltaFilePaths = 
deltaFiles.stream().map(Pair::getKey).collect(Collectors.toList());
+          SstFileSetReader sstFileSetReader = new 
SstFileSetReader(deltaFilePaths);
+          fileToBeIngested = differTmpDir.resolve(table + "-" + 
UUID.randomUUID() + SST_FILE_EXTENSION);
+          // Delete all delta files after reingesting into the checkpointStore.
+          filesToBeDeleted.add(fileToBeIngested);
+          int deltaEntriesCount = 0;
+          try (ClosableIterator<String> keysToCheck =
+                   
sstFileSetReader.getKeyStreamWithTombstone(sstFileReaderLowerBound, 
sstFileReaderUpperBound);
+               TableMergeIterator<String, byte[]> tableMergeIterator = new 
TableMergeIterator<>(keysToCheck,
+                  tableBucketPrefix, snapshotTable, previousSnapshotTable);
+               RDBSstFileWriter rdbSstFileWriter = new 
RDBSstFileWriter(fileToBeIngested.toFile())) {
+            while (tableMergeIterator.hasNext()) {
+              Table.KeyValue<String, List<byte[]>> kvs = 
tableMergeIterator.next();
+              // Check if the values are equal or if they are not equal then 
the value should be written to the
+              // delta sstFile.
+              if (!Arrays.equals(kvs.getValue().get(0), 
kvs.getValue().get(1))) {
+                try (CodecBuffer key = 
StringCodec.get().toHeapCodecBuffer(kvs.getKey())) {
+                  byte[] keyArray = key.asReadOnlyByteBuffer().array();
+                  byte[] val = kvs.getValue().get(0);
+                  // If the value is null then add a tombstone to the delta 
sstFile.
+                  if (val == null) {
+                    rdbSstFileWriter.delete(keyArray);
+                  } else {
+                    rdbSstFileWriter.put(keyArray, val);
+                  }
+                }
+                deltaEntriesCount++;
+              }
+            }
+          } catch (RocksDBException e) {
+            throw new RocksDatabaseException("Error while reading sst files.", 
e);
+          }
+          if (deltaEntriesCount == 0) {
+            // If there are no delta entries then delete the delta file. No 
need to ingest the file as a diff.
+            fileToBeIngested = null;
+          }
+        }
+        if (fileToBeIngested != null) {
+          if (!fileToBeIngested.toFile().exists()) {
+            throw new IOException("Delta file does not exist: " + 
fileToBeIngested);
+          }
+          Table checkpointTable = checkpointStore.getTable(table);
+          checkpointTable.loadFromFile(fileToBeIngested.toFile());
+        }
+      }
+    } finally {
+      for (Path path : filesToBeDeleted) {
+        if (path.toFile().exists()) {
+          if (!path.toFile().delete()) {
+            LOG.warn("Failed to delete file: {}", path);
+          }
+        }
+      }
+    }
+  }
 
-    // TODO: Implement incremental defragmentation
+  /**
+   * Ingests non-incremental tables from a snapshot into a checkpoint database 
store.
+   * This involves exporting table data from the snapshot to intermediate SST 
files
+   * and ingesting them into the corresponding tables in the checkpoint 
database store.
+   * Tables that are part of incremental defragmentation are excluded from 
this process.
+   *
+   * @param checkpointDBStore the database store where non-incremental tables 
are ingested.
+   * @param snapshotInfo the metadata information of the snapshot being 
processed.
+   * @param bucketPrefixInfo prefix information used for determining table 
prefixes.
+   * @param incrementalTables the set of tables identified for incremental 
defragmentation.
+   * @throws IOException if an I/O error occurs during table ingestion or file 
operations.
+   */
+  private void ingestNonIncrementalTables(DBStore checkpointDBStore,
+      SnapshotInfo snapshotInfo, TablePrefixInfo bucketPrefixInfo, Set<String> 
incrementalTables) throws IOException {
+    String volumeName = snapshotInfo.getVolumeName();
+    String bucketName = snapshotInfo.getBucketName();
+    String snapshotName = snapshotInfo.getName();
+    Set<Path> filesToBeDeleted = new HashSet<>();
+    try (UncheckedAutoCloseableSupplier<OmSnapshot> snapshot = 
omSnapshotManager.getActiveSnapshot(volumeName,
+        bucketName, snapshotName)) {
+      DBStore snapshotDBStore = snapshot.get().getMetadataManager().getStore();
+      for (Table snapshotTable : snapshotDBStore.listTables()) {
+        String snapshotTableName = snapshotTable.getName();
+        if (!incrementalTables.contains(snapshotTable.getName())) {
+          Path tmpSstFile = differTmpDir.resolve(snapshotTable.getName() + "-" 
+ UUID.randomUUID()
+              + SST_FILE_EXTENSION);
+          filesToBeDeleted.add(tmpSstFile);
+          String prefix = bucketPrefixInfo.getTablePrefix(snapshotTableName);
+          byte[] prefixBytes = Strings.isBlank(prefix) ? null : 
StringCodec.get().toPersistedFormat(prefix);
+          Table<byte[], byte[]> snapshotTableBytes = 
snapshotDBStore.getTable(snapshotTableName, ByteArrayCodec.get(),
+              ByteArrayCodec.get());
+          snapshotTableBytes.dumpToFileWithPrefix(tmpSstFile.toFile(), 
prefixBytes);
+          Table<byte[], byte[]> checkpointTable = 
checkpointDBStore.getTable(snapshotTableName, ByteArrayCodec.get(),
+              ByteArrayCodec.get());
+          checkpointTable.loadFromFile(tmpSstFile.toFile());
+        }
+      }
+    } finally {
+      for (Path path : filesToBeDeleted) {
+        if (path.toFile().exists()) {
+          if (!path.toFile().delete()) {
+            LOG.warn("Failed to delete file for ingesting non incremental 
table: {}", path);
+          }
+        }
+      }
+    }
+  }
+
+  /**
+   * Atomically switches the snapshot database to a new version by moving the
+   * checkpoint directory to the next version directory and updating relevant
+   * metadata. Ensures data consistency and manages cleanup of older versions.
+   *
+   * @param snapshotId Unique identifier of the snapshot to switch.
+   * @param checkpointPath Path to the checkpoint directory that will be moved
+   *                       to the new version directory.
+   * @throws IOException If an error occurs during directory operations,
+   *                     metadata management, lock acquisition, or database 
access.
+   */
+  private void atomicSwitchSnapshotDB(UUID snapshotId, Path checkpointPath) 
throws IOException {
+    int previousVersion;
+    try (WritableOmSnapshotLocalDataProvider snapshotLocalDataProvider =
+             
snapshotLocalDataManager.getWritableOmSnapshotLocalData(snapshotId)) {
+      OmSnapshotLocalData localData = 
snapshotLocalDataProvider.getSnapshotLocalData();
+      Path nextVersionPath = 
OmSnapshotManager.getSnapshotPath(ozoneManager.getMetadataManager(), snapshotId,
+          localData.getVersion() + 1);
+      // Remove the directory if it exists.
+      if (nextVersionPath.toFile().exists()) {
+        deleteDirectory(nextVersionPath);
+      }
+      // Move the checkpoint directory to the next version directory.
+      Files.move(checkpointPath, nextVersionPath);
+      RocksDBCheckpoint dbCheckpoint = new RocksDBCheckpoint(nextVersionPath);
+      // Add a new version to the local data file.
+      try (OmMetadataManagerImpl newVersionCheckpointMetadataManager =
+               OmMetadataManagerImpl.createCheckpointMetadataManager(conf, 
dbCheckpoint, true)) {
+        RDBStore newVersionCheckpointStore = (RDBStore) 
newVersionCheckpointMetadataManager.getStore();
+        
snapshotLocalDataProvider.addSnapshotVersion(newVersionCheckpointStore);
+        snapshotLocalDataProvider.commit();
+      }
+      previousVersion = localData.getVersion() - 1;
+    }
+
+    // Binary search smallest existing version and delete the older versions 
starting from the smallest version.
+    // This is to ensure efficient crash recovery.
+    int smallestExistingVersion = 0;
+    int largestExistingVersion = previousVersion;
+    while (smallestExistingVersion <= largestExistingVersion) {
+      int midVersion = smallestExistingVersion + (largestExistingVersion - 
smallestExistingVersion) / 2;
+      Path path = 
OmSnapshotManager.getSnapshotPath(ozoneManager.getMetadataManager(), 
snapshotId, midVersion);
+      if (path.toFile().exists()) {
+        largestExistingVersion = midVersion - 1;
+      } else {
+        smallestExistingVersion = midVersion + 1;
+      }
+    }
+
+    // Acquire Snapshot DBHandle lock before removing the older version to 
ensure all readers are done with the
+    // snapshot db use.
+    try (UncheckedAutoCloseableSupplier<OMLockDetails> lock =
+             
ozoneManager.getOmSnapshotManager().getSnapshotCache().lock(snapshotId)) {
+      if (!lock.get().isLockAcquired()) {
+        throw new IOException("Failed to acquire dbHandlelock on snapshot: " + 
snapshotId);
+      }
+      // Delete the older version directories. Always starting deletes from 
smallest version to largest version to
+      // ensure binary search works correctly on a later basis.
+      for (int version = smallestExistingVersion; version <= previousVersion; 
version++) {
+        Path path = 
OmSnapshotManager.getSnapshotPath(ozoneManager.getMetadataManager(), 
snapshotId, version);
+        deleteDirectory(path);
+      }
+    }

Review Comment:
   I would extract these lines into a method cleanupAndReleaseOlderVersions()



##########
hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/defrag/SnapshotDefragService.java:
##########
@@ -192,6 +527,103 @@ public BackgroundTaskResult call() throws Exception {
     }
   }
 
+  /**
+   * Creates a new checkpoint by modifying the metadata manager from a 
snapshot.
+   * This involves generating a temporary checkpoint and truncating specified
+   * column families from the checkpoint before returning the updated metadata 
manager.
+   *
+   * @param snapshotInfo Information about the snapshot for which the 
checkpoint
+   *                     is being created.
+   * @param incrementalColumnFamilies A set of table names representing 
incremental
+   *                                   column families to be retained in the 
checkpoint.
+   * @return A new instance of OmMetadataManagerImpl initialized with the 
modified
+   *         checkpoint.
+   * @throws IOException If an I/O error occurs during snapshot processing,
+   *                     checkpoint creation, or table operations.
+   */
+  private OmMetadataManagerImpl createCheckpoint(SnapshotInfo snapshotInfo,
+      Set<String> incrementalColumnFamilies) throws IOException {
+    try (UncheckedAutoCloseableSupplier<OmSnapshot> snapshot = 
omSnapshotManager.getActiveSnapshot(
+        snapshotInfo.getVolumeName(), snapshotInfo.getBucketName(), 
snapshotInfo.getName())) {
+      DBCheckpoint checkpoint = 
snapshot.get().getMetadataManager().getStore().getCheckpoint(tmpDefragDir, 
true);
+      try (OmMetadataManagerImpl metadataManagerBeforeTruncate =
+               OmMetadataManagerImpl.createCheckpointMetadataManager(conf, 
checkpoint, false)) {
+        DBStore dbStore = metadataManagerBeforeTruncate.getStore();
+        for (String table : metadataManagerBeforeTruncate.listTableNames()) {
+          if (!incrementalColumnFamilies.contains(table)) {
+            dbStore.dropTable(table);
+          }
+        }
+      } catch (Exception e) {
+        throw new IOException("Failed to close checkpoint of snapshot: " + 
snapshotInfo.getSnapshotId(), e);
+      }
+      // This will recreate the column families in the checkpoint.
+      return OmMetadataManagerImpl.createCheckpointMetadataManager(conf, 
checkpoint, false);
+    }
+  }
+
+  private void acquireContentLock(UUID snapshotID) throws IOException {
+    lockIds.clear();
+    lockIds.add(snapshotID);
+    OMLockDetails lockDetails = snapshotContentLocks.acquireLock(lockIds);
+    if (!lockDetails.isLockAcquired()) {
+      throw new IOException("Failed to acquire lock on snapshot: " + 
snapshotID);
+    }
+    LOG.debug("Acquired MultiSnapshotLocks on snapshot: {}", snapshotID);
+  }
+
+  private boolean checkAndDefragSnapshot(SnapshotChainManager chainManager, 
UUID snapshotId) throws IOException {
+    SnapshotInfo snapshotInfo = SnapshotUtils.getSnapshotInfo(ozoneManager, 
chainManager, snapshotId);
+
+    if (snapshotInfo.getSnapshotStatus() != 
SnapshotInfo.SnapshotStatus.SNAPSHOT_ACTIVE) {
+      LOG.debug("Skipping defragmentation for non-active snapshot: {} (ID: 
{})",
+          snapshotInfo.getName(), snapshotInfo.getSnapshotId());
+      return false;
+    }
+    Pair<Boolean, Integer> needsDefragVersionPair = 
needsDefragmentation(snapshotInfo);
+    if (!needsDefragVersionPair.getLeft()) {
+      return false;
+    }
+    // Create a checkpoint of the previous snapshot or the current snapshot if 
it is the first snapshot in the chain.
+    SnapshotInfo checkpointSnapshotInfo = 
snapshotInfo.getPathPreviousSnapshotId() == null ? snapshotInfo :
+        SnapshotUtils.getSnapshotInfo(ozoneManager, chainManager, 
snapshotInfo.getPathPreviousSnapshotId());
+
+    OmMetadataManagerImpl checkpointMetadataManager = 
createCheckpoint(checkpointSnapshotInfo,
+        COLUMN_FAMILIES_TO_TRACK_IN_SNAPSHOT);
+    Path checkpointLocation = 
checkpointMetadataManager.getStore().getDbLocation().toPath();
+    try {
+      DBStore checkpointDBStore = checkpointMetadataManager.getStore();
+      TablePrefixInfo prefixInfo = 
ozoneManager.getMetadataManager().getTableBucketPrefix(snapshotInfo.getVolumeName(),
+          snapshotInfo.getBucketName());
+      // If first snapshot in the chain perform full defragmentation.
+      if (snapshotInfo.getPathPreviousSnapshotId() == null) {
+        performFullDefragmentation(checkpointDBStore, prefixInfo, 
COLUMN_FAMILIES_TO_TRACK_IN_SNAPSHOT);
+      } else {
+        performIncrementalDefragmentation(checkpointSnapshotInfo, 
snapshotInfo, needsDefragVersionPair.getValue(),
+            checkpointDBStore, prefixInfo, 
COLUMN_FAMILIES_TO_TRACK_IN_SNAPSHOT);
+      }
+
+      // Acquire Content lock on the snapshot to ensure the contents of the 
table doesn't get changed.
+      acquireContentLock(snapshotId);
+      try {
+        // Ingestion of incremental tables KeyTable/FileTable/DirectoryTable 
done now we need to just reingest the
+        // remaining tables from the original snapshot.
+        ingestNonIncrementalTables(checkpointDBStore, snapshotInfo, 
prefixInfo, COLUMN_FAMILIES_TO_TRACK_IN_SNAPSHOT);
+        checkpointMetadataManager.close();
+        // Switch the snapshot DB location to the new version.
+        atomicSwitchSnapshotDB(snapshotId, checkpointLocation);
+      } finally {
+        snapshotContentLocks.releaseLock();

Review Comment:
   it may hold snapshot content lock for a long time if defrag service waits 
for the previous snapshot cache lock. What if we delay the clean-up of older 
versions after the release of snapshot content lock?



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