Github user hanm commented on a diff in the pull request:
    --- Diff: 
src/java/main/org/apache/zookeeper/server/persistence/ ---
    @@ -165,8 +165,22 @@ public File getSnapDir() {
         public long restore(DataTree dt, Map<Long, Integer> sessions,
                 PlayBackListener listener) throws IOException {
    -        snapLog.deserialize(dt, sessions);
    +        long deserializeResult = snapLog.deserialize(dt, sessions);
             FileTxnLog txnLog = new FileTxnLog(dataDir);
    +        if (-1L == deserializeResult) {
    +            /* this means that we couldn't find any snapshot, so we need to
    +             * initialize an empty database */
    +            if (txnLog.getLastLoggedZxid() != -1) {
    +                throw new IOException(
    +                        "No snapshot found, but there are log entries. " +
    +                        "Something is broken!");
    +            }
    +            /* TODO: (br33d) we should either put a ConcurrentHashMap on 
    +             *       or use Map on save() */
    +            save(dt, (ConcurrentHashMap<Long, Integer>)sessions);
    --- End diff --
    I think we need it here because if we are getting here then the zxid of 
this server must be -1, so it would not win leader election if at least one 
other server is sane (with valid snapshot/txn log to recover.), so this server 
will become a follow and sync the (none empty) snapshot from the leader. If all 
servers have empty snapshots then this save is also required to bootstrap the 
recover process.

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