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From "Bryan Pendleton (JIRA)" <derby-...@db.apache.org>
Subject [jira] Updated: (DERBY-1219) jdbcapi/checkDataSource.java and jdbcapi/checkDataSource30.java hang intermittently with client
Date Wed, 10 May 2006 04:31:10 GMT
     [ http://issues.apache.org/jira/browse/DERBY-1219?page=all ]

Bryan Pendleton updated DERBY-1219:
-----------------------------------

    Attachment: no-sessions-for-closed-threads.diff

Hi Deepa,
I think that your scenarios are excellent, and they definitely demonstrate the problems in
this area. 
I think that the fun thing about a bug like this, is that there are many possible scenarios.
:)

The one I was concentrating on is a bit different from yours, so let me try to diagram it
as follows:

1) Some thread is idling, blocked in NetworkServerControlImpl.getNextSession() as called by
   DRDAConnThread.run(). I think this is the standard place for a thread to block when it
is idle.

2) Server restart occurs, and runs straight through to completion. This results in calling
close()
   on the thread from point (1), and also removing that thread from the ThreadList. *But the
thread
   does not terminate.*

3) Some time later, some new connections start coming in. The first new connection, as you
   point out, will create a new thread to handle the session. The next new conection, however,
will
   find that a thread already exists, and so it will simply put the session onto the RunQueue
list.

4) The original thread then wakes up, grabs the session, notices that the thread has been
   closed, and exits.

The point I'm trying to make here is that no overlapping of actions is required, and the connection

does not have to arrive during the restart. 

It seems to me that, once a restart happens while 1 or more threads happen to be sitting idle,
blocked in their getNextSession() calls, then those threads are "poisoned", and there is
now a ticking time bomb in the server. At some point in the future, a session will get added
to the RunQueue, and one of these "poisoned" (closed) threads will grab the session, and
will then terminate prematurely without processing the session.

So the only place where I differ with your analysis, I believe, is that I think it is *not*
okay to
leave these threads out there, marked as closed, because at some point in the future the
threads will grab sessions off the run queue and fail to process them.

So I think one crucial thing to ensure is that, once a thread is marked as closed, it will
no 
longer pick up a new session to process.

With that in mind, I've experimented with yet another patch, called "no-sessions-for-closed-threads.diff",
which attempts to prevent threads marked as closed from fetching sessions to process.

It seems to resolve the hang for me, but I haven't exhaustively tested it. Still, I thought
it
showed enough promise to attach for you to examine.


> jdbcapi/checkDataSource.java and jdbcapi/checkDataSource30.java hang intermittently with
client
> -----------------------------------------------------------------------------------------------
>
>          Key: DERBY-1219
>          URL: http://issues.apache.org/jira/browse/DERBY-1219
>      Project: Derby
>         Type: Test

>   Components: Network Server, Network Client
>     Versions: 10.2.0.0
>  Environment: More often on jdk 1.5 or jdk 1.6 but hangs on jdk 1.4.2 as well
>     Reporter: Kathey Marsden
>     Assignee: Bryan Pendleton
>     Priority: Minor
>  Attachments: client_stack_trace_050306.txt, drda_traces_050206.zip, interrupt.diff,
no-sessions-for-closed-threads.diff, server_stack_trace_050306.txt, skipThreads.diff, testfiles_afterhang.zip,
traces_on_hang.txt
>
> The tests checkDataSource.java and checkDataSource30.java 
> hang intermittently especially with jdk 1.5.
> Attached is the test run output and traces when the server is started separately.
> 1) Enable checkDataSource30.java by taking it out of functionTests/suites/DerbyNetClient.exclude.
> 2) Run the test with client.
> java -Dij.exceptionTrace=true -Dkeepfiles=true -Dframework=DerbyNetClient org.apache.derbyTesting.functionTests.harness.RunTest
jdbcapi/checkDataSource30.java
> Attachements:
>  testfiles_after_hang.zip - Test directory.
>  traces_on_hang.txt  - Server side traces obtained by starting the server separately
before running the test.
> I wish I had time to work on this right now as I would really like to see this valuable
test in the suite, but hopefully someone else will pick it up.

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