Github user arunmahadevan commented on a diff in the pull request:

    https://github.com/apache/storm/pull/1470#discussion_r68537734
  
    --- Diff: 
external/storm-redis/src/main/java/org/apache/storm/redis/state/RedisKeyValueState.java
 ---
    @@ -161,7 +176,11 @@ public void prepareCommit(long txid) {
                 commands = jedisContainer.getInstance();
                 if (commands.exists(prepareNamespace)) {
                     LOG.debug("Prepared txn already exists, will merge", txid);
    -                pendingPrepare.putAll(pendingCommit);
    +                for (Map.Entry<String, String> e: 
pendingCommit.entrySet()) {
    +                    if (!pendingPrepare.containsKey(e.getKey())) {
    +                        pendingPrepare.put(e.getKey(), e.getValue());
    +                    }
    +                }
                 }
                 if (!pendingPrepare.isEmpty()) {
                     commands.hmset(prepareNamespace, pendingPrepare);
    --- End diff --
    
    A potential issue (already existing) which could be fixed here or in a 
separate JIRA. If the pendingPrepare is updated after the hmset but before its 
assigned to pendingCommit, the pendingCommit will not reflect the entities in 
prepareNamespace. I think if the pendingPrepare is snapshotted/copied before 
hmset and the copy is used for both hmset and assigned to pendingCommit it 
would avoid this race condition.


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