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Re: 5.3 CLOSE_WAIT problem and multi instance change notification
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Re: 5.3 CLOSE_WAIT problem and multi instance change notification


  • Subject: Re: 5.3 CLOSE_WAIT problem and multi instance change notification
  • From: Hordur Thordarson <email@hidden>
  • Date: Wed, 12 Oct 2005 06:50:57 +0000

Hi Chuck,

Thanks very much for your answers ! I promise I'll buy your book now :-)

Just a few more questions:

1) At the risk of exposing my ignorance, how do I get a thread dump from a running java app, preferably via Terminal ?

2) I've never really liked the idea of change notification to sync app instances so your proposal sounds very good to me. And indeed reading Apples EO documentation it appears they agree with you. (Btw, their documentation has improved enormously since the last time I was doing WO, 4-5 years ago !!).
So, how would you handle the simple (or not) case of two app instances sharing a database and one instance updates an object and some related objects that both have previously read and cached ?
If they don't communicate the change with change notification then the only ways I can see are the ones suggested by you/Apple:
- Timed invalidation via EO(F)'s fetch timestamps
- Always refreshing using refreshObject or setRefreshesFetchedObjects
- The bulldozer way, invalidateAllObjects


My test case is a CMS with a Direct Action based front end (display) and a Component based back end (editing). If I'm running two instances of the app and I open up two browser windows, one displaying a page from the CMS and the other for editing that page, then every time I refresh the DA page I'll switch app instances due to round robin load balancing, so sometimes I'll be looking at data from the same instance I'm editing the page in which is easy to keep in sync, but sometimes I'll be looking at data from the other app instance, which is harder to keep fresh.

This scenario must occur fairly often in WO apps that allow editing of their and it would be great to hear how people are dealing with this.

Thanks again !

Hörður Þ.
Lausn hugbúnaður ehf
Tel. +354-534-5005 / +354-699-1068
Web: http://www.lausn.is


On 11.10.2005, at 22:57, Chuck Hill wrote:

Hi,

On Oct 11, 2005, at 11:52 AM, Hordur Thordarson wrote:

Hi all,

I have a client who is running an app of mine on OSX Server 10.4 with WebObjects 5.3, and recently we've been having significant problems with the app, probably as the load on the app has been increasing.

Currently there is just 1 instance of the application running. It will run fine for a while after being restarted, but then the app will go into a state where according to top it has > 100 threads as opposed to around 40-70 normally, and it will become unresponsive. Doing a netstat at this point in time shows a lot of connections in a CLOSE_WAIT state and the only way out is to kill the instance and restart the WebObjects service.

Is anyone seeing anything like this with OSX Server 10.4 and WO 5.3 ?

Not normally, but your description of > 100 threads sounds like it is deadlocked somewhere. Have you tried getting a thread dump?


Also, I was wondering if maybe running multiple instances would help with this

Even having 40 - 70 threads in one instance says that you want to be running multiple instances. That many threads indicates that something is blocking / deadlocking or that that instance is way overloaded.



and wanted to ask what people here are using for multi-instance db change notification. I've read about Project Wonder's ERChangeNotificationJMS and there is some old code from David Neumann of Apple floating around but that's all I've been able to find. Are you guys using ERChangeNotificationJMS or are you using homegrown stuff for multi instance sync ?

ERChangeNotificationJMS is a modern version of David Neumann's code. If I was going to use such a notification system that is the one that I would choose. So far, I have not found it to be necessary. You need to plan for object freshness and create new editing contexts / do refreshing fetches to ensure that you have data as fresh as you need it. You also need to take care of optimistic locking conflicts, but those can also happen when using a change notification system.

Chuck

--
Coming in 2006 - an introduction to web applications using WebObjects and Xcode http://www.global-village.net/wointro


Practical WebObjects - for developers who want to increase their overall knowledge of WebObjects or who are trying to solve specific problems. http://www.global-village.net/products/practical_webobjects





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