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Subject [GitHub] [zookeeper] hanm commented on a change in pull request #1069: ZOOKEEPER-3056: Fails to load database with missing snapshot file but with valid transaction log file.
Date Fri, 30 Aug 2019 22:32:55 GMT
hanm commented on a change in pull request #1069: ZOOKEEPER-3056: Fails to load database with
missing snapshot file but with valid transaction log file.
URL: https://github.com/apache/zookeeper/pull/1069#discussion_r319691423
 
 

 ##########
 File path: zookeeper-server/src/main/java/org/apache/zookeeper/server/persistence/FileTxnSnapLog.java
 ##########
 @@ -232,11 +242,19 @@ public long restore(DataTree dt, Map<Long, Integer> sessions,
PlayBackListener l
         } else {
             trustEmptyDB = autoCreateDB;
         }
+
         if (-1L == deserializeResult) {
             /* this means that we couldn't find any snapshot, so we need to
              * initialize an empty database (reported in ZOOKEEPER-2325) */
             if (txnLog.getLastLoggedZxid() != -1) {
-                throw new IOException("No snapshot found, but there are log entries. " +
"Something is broken!");
+                // ZOOKEEPER-3056: provides an escape hatch for users upgrading
+                // from old versions of zookeeper (3.4.x, pre 3.5.3).
+                if (!trustEmptySnapshot) {
+                    throw new IOException(EMPTY_SNAPSHOT_WARNING + "Something is broken!");
+                } else {
+                    LOG.warn(EMPTY_SNAPSHOT_WARNING + "This should only be allowed during
upgrading.");
+                    trustEmptySnapshot = false;
 
 Review comment:
   >> during internal reloads of the database
   
   database will only be loaded once from disk during a process's life time now we don't clear
the in memory data base anymore every time a server (object) restarts; so this is less a concern.

   
   >> I wonder if there is a cleaner way to allow this special case only during "start"
and not during all of the other code paths
   
   "start" and "other code paths" are no different, from server point of view they are all
recovery cases, be it a first start up or recovery from faults. So if we care about empty
snapshot, we should check in all places. If we ignore empty snapshot, we should ignore in
all places. The check logic and the skip check logic should be co-located, so refactoring
sequence of start ups will not impact that.

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