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Subject [GitHub] [zookeeper] eolivelli 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 19:44:23 GMT
eolivelli 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_r319645045
 
 

 ##########
 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:
   I am not an expert of this part, just want to share my doubts
   
   Ideally we will hit the case of the issue only while the server is starting up, not during
internal reloads of the database, it is allowed to have such lack of snapshot file only during
bootstrap.
   For instance I see that this method ("restore") is called in QuorumPeer#getLastLoggedZxid()
   if we refactor the code in the future and change the boot sequence this change won't take
effect.
   
   
   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 that leads to the invocations of this method.
   

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