Re: 5.3 CLOSE_WAIT problem and multi instance change notification
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 18:33:57 +0000
On 12.10.2005, at 18:26, Chuck Hill wrote:
On Oct 12, 2005, at 11:18 AM, Hordur Thordarson wrote:
<snip>
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
This applies only to the first fetch/fault of an object into an
editing context or subsequent refaulting of particular objects.
Hmm, sounds like I need to re-read this. I was assuming that
functioned like so given a 60 minute refetch timeout:
- An app requests an EO for the first time and it gets fetched from
the db and gets the current timestamp
- 30 minutes later the app re-requests the EO and gets the cached
version from the object graph
- 2 hrs down the road the app re-requests again and EOF then goes to
the db again as the EO is over 60 minutes old in the cache
Am I misunderstanding this ?
Yes. :-) This has _nothing_ to do with the application. It only
applies to editing context's getting a copy of the data from the DB
snapshots and asking that it receive nothing older than X. Once the
EC has that copy of the data, the age of the data is not considered
again unless the object is re-faulted / invalidated. Creating new ECs
frequently and avoiding the long lived session.defaultEditingContext()
will result in much fresher data.
<LIGHT GOES ON/>
Ok I get it now :-) I thought the other functionality sounded pretty
great ! Automatic timebased re-fetching of objects into an EC, not
only into the DB snapshots...
Anyway, I see what you are saying now re. diligent EC creation rather
than storing a monster EC somewhere. If there weren't a single,
global, application EC but rather f.ex. an EC for each DA request then
this timestamping would work the way I thought it would, right ?
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.
Someone else (Ken?) already gave you my answer for this: a preview
URL. Keep the editor and preview in the same session so that they
see the same data. For regular viewers, they can get fresh data
when their session is created / when they first look at something.
After that, they see what they originally saw, the information does
not change on them as they browse. That may or may not work for
you.
Uti had some suggestioins and it sounds like the only way of doing
this is to make sure the preview url contains the same app number and
session id as the user's editing session. Unfortunately users are
not the easiest bunch of people to control so inevitably they will
first load a web page through the front end, and then go edit it in
another window in the backend (and possibly in another app instance),
and then they will scream when they refresh the original page and
their changes don't show up :-)
One word. Cookies. This is what cookies are for. They preserve
state without requiring URL changes. Cookies will ensure that the
front end and back end windows share the same instance and session.
Cookies are not evil. Cookies are your friend.
Ok ok, sounds like cookies are the way to go, I'll remember that :-)
Thanks !
Hordur
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
--
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
--
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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