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From "Sorabh Hamirwasia (JIRA)" <j...@apache.org>
Subject [jira] [Assigned] (DRILL-5721) Query with only root fragment and no non-root fragment hangs when Drillbit to Drillbit Control Connection has network issues
Date Mon, 21 Aug 2017 18:20:00 GMT

     [ https://issues.apache.org/jira/browse/DRILL-5721?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sorabh Hamirwasia reassigned DRILL-5721:
----------------------------------------

    Assignee: Sorabh Hamirwasia

> Query with only root fragment and no non-root fragment hangs when Drillbit to Drillbit
Control Connection has network issues
> ----------------------------------------------------------------------------------------------------------------------------
>
>                 Key: DRILL-5721
>                 URL: https://issues.apache.org/jira/browse/DRILL-5721
>             Project: Apache Drill
>          Issue Type: Bug
>            Reporter: Sorabh Hamirwasia
>            Assignee: Sorabh Hamirwasia
>
> Recently I found an issue (Thanks to [~knguyen] to create this scenario) related to Fragment
Status reporting and would like some feedback on it. 
> When a client submits a query to Foreman, then it is planned by Foreman and later fragments
are scheduled to root and non-root nodes. Foreman creates a DriilbitStatusListener and FragmentStatusListener
to know about the health of Drillbit node and a fragment respectively. The way root and non-root
fragments are setup by Foreman are different: 
> Root fragments are setup without any communication over control channel (since it is
executed locally on Foreman)
> Non-root fragments are setup by sending control message (REQ_INITIALIZE_FRAGMENTS_VALUE)
over wire. If there is failure in sending any such control message (like due to network hiccup's)
during query setup then the query is failed and client is notified. 
> Each fragment is executed on it's node with the help Fragment Executor which has an instance
for FragmentStatusReporter. FragmentStatusReporter helps to update the status of a fragment
to Foreman node over a control tunnel or connection using RPC message (REQ_FRAGMENT_STATUS)
both for root and non-root fragments. 
> Based on above when root fragment is submitted for setup then it is done locally without
any RPC communication whereas when status for that fragment is reported by fragment executor
that happens over control connection by sending a RPC message. But for non-root fragment setup
and status update both happens using RPC message over control connection.
> *Issue 1:*
> What was observed is if for a simple query which has only 1 root fragment running on
Foreman node then setup will work fine. But as part of status update when the fragment tries
to create a control connection and fails to establish that, then the query hangs. This is
because the root fragment will complete execution but will fail to update Foreman about it
and Foreman think that the query is running for ever. 
> *Proposed Solution:*
> For root fragment the setup of fragment is happening locally without RPC message, so
we can do the same for status update of root fragments. This will avoid RPC communication
for status update of fragments running locally on the foreman and hence will resolve issue
1.



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