[GitHub] [ozone] GeorgeJahad commented on a diff in pull request #3658: HDDS-6983. Snapshot Chain - list of snapshots per snapshottable bucket

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

GeorgeJahad commented on code in PR #3658:
URL: https://github.com/apache/ozone/pull/3658#discussion_r942944316


##########
hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/SnapshotChainManager.java:
##########
@@ -0,0 +1,446 @@
+/*
+ * 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;
+
+import com.google.common.annotations.VisibleForTesting;
+import org.apache.hadoop.hdds.utils.db.Table;
+import org.apache.hadoop.hdds.utils.db.TableIterator;
+import org.apache.hadoop.ozone.om.helpers.SnapshotInfo;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.LinkedHashMap;
+import java.util.TreeMap;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This class is used for creating and accessing Snapshot Chains.
+ *
+ * The snapshot chain maintains the in-memory sequence of snapshots
+ * created in chronological order.  There are two such snapshots maintained
+ * i.) Path based snapshot chain, sequence of snapshots created for a
+ * given /volume/bucket
+ * ii.) Global snapshot chain, sequence of all snapshots created in order
+ *
+ * On start, the snapshot chains are initialized from the on disk
+ * SnapshotInfoTable from the om RocksDB.
+ */
+public class SnapshotChainManager {
+  private LinkedHashMap<String, SnapshotChainInfo>  snapshotChainGlobal;
+  private Map<String, LinkedHashMap<String, SnapshotChainInfo>>
+      snapshotChainPath;
+  private Map<String, String> latestPathSnapshotID;
+  private String latestGlobalSnapshotID;
+  private static final Logger LOG =
+      LoggerFactory.getLogger(SnapshotChainManager.class);
+
+  public SnapshotChainManager(OMMetadataManager metadataManager)
+          throws IOException {
+    snapshotChainGlobal = new LinkedHashMap<>();
+    snapshotChainPath = new HashMap<>();
+    latestPathSnapshotID = new HashMap<>();
+    latestGlobalSnapshotID = null;
+    loadFromSnapshotInfoTable(metadataManager);
+  }
+
+  private void addSnapshotGlobal(String snapshotID,
+                            String prevGlobalID) throws IOException {
+    // set previous snapshotID to null if it is "" for
+    // internal in-mem structure
+    if (prevGlobalID != null && prevGlobalID.equals("")) {
+      prevGlobalID = null;
+    }
+    // on add snapshot; set previous snapshot entry nextSnapshotID =
+    // snapshotID
+    if (prevGlobalID != null &&
+        snapshotChainGlobal.containsKey(prevGlobalID)) {
+      snapshotChainGlobal
+          .get(prevGlobalID)
+          .setNextSnapshotID(snapshotID);
+    }
+    if (prevGlobalID != null &&
+        !snapshotChainGlobal.containsKey(prevGlobalID)) {
+      throw new IOException("Snapshot Chain corruption: "
+          + " previous snapshotID given but no associated snapshot "
+      + "found in snapshot chain: SnapshotID "
+      + prevGlobalID);
+    }
+    snapshotChainGlobal.put(snapshotID,

Review Comment:
   The snapshot UUID is used as the key to the Global snapshot chain and the individual path chain maps.  That works but seems overly complicated?  
   
   Why not just use the same key that the snapshotInfo table uses, (snapshotPath + name)?  That eliminates the need to do an extra lookup to get the UUID.
   



-- 
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

To unsubscribe, e-mail: issues-unsubscribe@ozone.apache.org

For queries about this service, please contact Infrastructure at:
users@infra.apache.org


---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscribe@ozone.apache.org
For additional commands, e-mail: issues-help@ozone.apache.org