[jira] [Commented] (SAMZA-1655) StreamProcessor skips all events from zookeeper server after zkClient session expiration.

["Prateek Maheshwari (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SAMZA-1655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16796394#comment-16796394 ] 

Prateek Maheshwari commented on SAMZA-1655:
-------------------------------------------

[~spvenkat] Is this still an issue?

> StreamProcessor skips all events from zookeeper server after zkClient session expiration.
> -----------------------------------------------------------------------------------------
>
>                 Key: SAMZA-1655
>                 URL: https://issues.apache.org/jira/browse/SAMZA-1655
>             Project: Samza
>          Issue Type: Bug
>            Reporter: Shanthoosh Venkataraman
>            Assignee: Shanthoosh Venkataraman
>            Priority: Major
>
> *Problem:*
> StreamProcessor skips all events from zookeeper server after zkClient session expiration.
> *Reason:*
> All the zkWatchers(dataChange, childChange handler) in a StreamProcessor are instantiated with an inmemory generationId(zkUtils.generationId).
> All the zkWatchers cache this generationId passed through the constructor.
> This inmemory generationId is incremented whenever the zkClient session expiration occurs.
> Any event from zookeeper server is dropped if the inmemory generationId is not equal to the generationId cached in a zkWatcher.
> After the zkClient session expiration in a StreamProcessor, this will result in zombie StreamProcessors and will stall message processing.
> In worst case, if this happens to the leader StreamProcessor then the whole processors group will be stalled.
> GenerationId was added to skip stale events going to handlers registered before a session expiration.
>  



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