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From "Naveen Nalam (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-255) Client Calls are not cancelled after a call timeout
Date Thu, 25 May 2006 22:31:29 GMT
Client Calls are not cancelled after a call timeout

         Key: HADOOP-255
         URL: http://issues.apache.org/jira/browse/HADOOP-255
     Project: Hadoop
        Type: Bug

  Components: ipc  
    Versions: 0.2.1    
 Environment: Tested on Linux 2.6
    Reporter: Naveen Nalam

In ipc/Client.java, if a call times out, a SocketTimeoutException is thrown but the Call object
still exists on the queue.

What I found was that when transferring very large amounts of data, it's common for queued
up calls to timeout. Yet even though the caller has is no longer waiting, the request is still
serviced on the server and the data is sent to the client. The client after receiving the
full response calls callComplete() which is a noop since nobody is waiting.

The problem is that the calls that timeout will retry and the system gets into a situation
where data is being transferred around, but it's all data for timed out requests and no progress
is ever made.

My quick solution to this was to add a "boolean timedout" to the Call object which I set to
true whenever the queued caller times out. And then when the client starts to pull over the
response data (in Connection::run) to first check if the Call is timedout and immediately
close the connection.

I think a good fix for this is to queue requests on the client, and do a single sendParam
only when there is no outstanding request. This will allow closing the connection when receiving
a response for a request we no longer have pending, reopen the connection, and resend the
next queued request. I can provide a patch for this, but I've seen a lot of recent activity
in this area so I'd like to get some feedback first.

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