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From Dejan Bosanac <de...@nighttale.net>
Subject Re: ajax delivery frequently gets delayed or stalled for 25 seconds in activemq 5.3
Date Thu, 15 Jul 2010 08:06:34 GMT
Hi Alex,

thanks for this thorough testing of new refactored Ajax API. I'm very
glad it works better then the old one. ActiveMQ 5.4.0 should be
released soon and all releases from that point on will include this
new implementation. There will be no more 5.3.x releases, so the old
implementation will not be maintained any more. Anyhow, the API is
refactored due to move from Jetty 6 to Jetty 7, which implied a change
in Continuation API used. As 5.3 branch is on Jetty 6, the code could
not be easily ported.

Cheers
--
Dejan Bosanac - http://twitter.com/dejanb

Open Source Integration - http://fusesource.com/
ActiveMQ in Action - http://www.manning.com/snyder/
Blog - http://www.nighttale.net



On Wed, Jul 14, 2010 at 5:24 PM, Alex Dean <adean@meteostar.com> wrote:
> The ajax servlet in 5.3 will often 'stall', and fail to deliver messages for
> about 25 seconds at a time.  This behavior is not present in the 5.4
> snapshots I've tried recently.  Everything seems to work perfectly with that
> code.  I've run tests up to a few hundred messages without missing one or
> having any of delays.  Dejan stated there has been some refactoring work
> going on in the ajax servlet code, and it seems like this has definitely
> improved things.
>
> I'm writing now:
>  1. as an FYI to other people who might be having problems with the ajax
> code in 5.3, and
>  2. to ask if it's possible that these 5.4 changes merged back into 5.3,
> since 5.4 is not yet stable/released.
>
> More details:
>
> I think that MessageListenerServlet is entering a sleeping/suspended state
> when it should not.
> http://fisheye6.atlassian.com/browse/activemq/branches/activemq-5.3/activemq-web/src/main/java/org/apache/activemq/web/MessageListenerServlet.java?r=HEAD
> In this link, line 72 sets "private long maximumReadTimeout = 25000;".  This
> is used in "continuation.suspend(timeout);" on line 301.  I'm not exactly
> sure why this is happening, but this timeout value very closely matches the
> delays I see in my message delivery.
>
> In my testing, I created an HTML/JavaScript page which uses the ActiveMQ
> ajax connector to subscribe to a topic, and then publish 1 message/second to
> this topic.  The first time the page loads, this works fine.  I receive
> messages immediately.  When I reload the page, however, it takes roughly 25
> seconds for the first message to arrive.  The first one I get is either #24
> or #25, and all previous messages are not delivered.  If I close the window
> and open a new one, message delivery is normal.  When I reload, I often see
> this initial delay happen.  I see this same behavior in the chat.html script
> which is included in ActiveMQ, so I'm pretty sure it's not a client-side
> issue.
>
> Sometimes, while messages are coming in normally, delivery will 'stall',
> again for about 25 seconds.  After this time has elapsed, all the missing
> messages are delivered at once.  In other words, I can get messages 1-10
> normally at a rate of approximately 1/second.  Then message #11 will fail to
> appear.  After 25 seconds, messages #11-#36 appear nearly simultaneously.
>  After than, delivery returns to the normal 1/second rate.
>
> Here's an example of what a 'stall' looks like.  The 'sent' and 'recd' times
> are in seconds since the page loaded.  Times are all calculated in
> javascript, so the same clock is in use for both.  'in-transit' is just recd
> minus sent.  Delivery is normal up to message 19, then messages 20-44 are
> delayed, then normal delivery resumes at message 45.  Messages 20-44 all
> appear at nearly the same moment.
>
> 50  sent:49.999, recd: 50.035, in-transit: 0.036
> 49  sent:48.997, recd: 49.032, in-transit: 0.035
> 48  sent:47.999, recd: 48.038, in-transit: 0.039
> 47  sent:46.992, recd: 47.028, in-transit: 0.036
> 46  sent:45.998, recd: 46.021, in-transit: 0.023
> 45  sent:44.997, recd: 45.023, in-transit: 0.026
> 44  sent:44, recd: 44.457, in-transit: 0.457
> 43  sent:43, recd: 44.446, in-transit: 1.446
> 42  sent:42, recd: 44.435, in-transit: 2.435
> 41  sent:40.999, recd: 44.424, in-transit: 3.425
> 40  sent:39.999, recd: 44.413, in-transit: 4.414
> 39  sent:39, recd: 44.403, in-transit: 5.403
> 38  sent:38, recd: 44.393, in-transit: 6.393
> 37  sent:37, recd: 44.382, in-transit: 7.382
> 36  sent:35.994, recd: 44.372, in-transit: 8.378
> 35  sent:34.998, recd: 44.362, in-transit: 9.364
> 34  sent:34.002, recd: 44.352, in-transit: 10.35
> 33  sent:32.993, recd: 44.342, in-transit: 11.349
> 32  sent:32, recd: 44.333, in-transit: 12.333
> 31  sent:31, recd: 44.324, in-transit: 13.324
> 30  sent:29.999, recd: 44.316, in-transit: 14.317
> 29  sent:28.999, recd: 44.308, in-transit: 15.309
> 28  sent:27.999, recd: 44.3, in-transit: 16.301
> 27  sent:27, recd: 44.293, in-transit: 17.293
> 26  sent:25.998, recd: 44.286, in-transit: 18.288
> 25  sent:24.994, recd: 44.278, in-transit: 19.284
> 24  sent:23.999, recd: 44.272, in-transit: 20.273
> 23  sent:23, recd: 44.265, in-transit: 21.265
> 22  sent:21.996, recd: 44.259, in-transit: 22.263
> 21  sent:21, recd: 44.252, in-transit: 23.252
> 20  sent:19.997, recd: 44.245, in-transit: 24.248
> 19  sent:19.001, recd: 19.198, in-transit: 0.197
> 18  sent:17.995, recd: 18.028, in-transit: 0.033
> 17  sent:16.991, recd: 17.025, in-transit: 0.034
> 16  sent:16.005, recd: 16.04, in-transit: 0.035
> 15  sent:15.004, recd: 15.037, in-transit: 0.033
> 14  sent:14.01, recd: 14.04, in-transit: 0.03
> 13  sent:13.001, recd: 13.026, in-transit: 0.025
> 12  sent:12, recd: 12.027, in-transit: 0.027
> 11  sent:10.999, recd: 11.032, in-transit: 0.033
> 10  sent:9.998, recd: 10.024, in-transit: 0.026
>
> While this 'stall' is happening, if I reload the page (either by clicking
> 'reload', or by focusing on the browser's address bar and hitting 'enter'),
> the stalled messages are immediately delivered.  So, if the stall happens
> after message 10, then I wait 5 seconds and reload, I see messages 11-15
> displayed just before the browser reloads.  I'm guessing that when the
> client closes the open GET request which is parked on the server, that
> somehow causes the server to flush queued/suspended messages back to the
> client.  Why they get queued/suspended in the first place is really the
> question.
>
> thanks,
> alex
>
>
>

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