[Seaside] production systems experiences
julian at beta4.com
Tue May 4 19:02:26 CEST 2004
radoslav hodnicak wrote:
> I have one seaside/squeak system running in production, it ran
> trouble-free for weeks, but today I've seen some very strange behaviour
> that I can't explain from looking at my code - it looks like some action
> blocks got somehow triggered twice. I know that mixing blocks,
> continuations, exceptions etc is messy - has anyone seen similar problems?
> Any tips how to (try) to diagnose this?
Hmm... it's hard to see how that could happen although I do have
memories of seeing it occasionaly in the past. This is still 2.3? I
wonder whether you had some processes terminated which left the blocks
marked as if there was still code executing them or something? The
session should be protected by WAProcessMonitor to make sure that two
requests are never running in the same session at the same time. There
are a few problems with concurrency under high load in 2.3. I fixed
these at work and merged the fixes into 2.5 but should probably look at
pushing them into 2.3 as well... so if you were getting quite heavy
load (we were testing with 20 concurrent users hitting it pretty hard)
that could also be your problem possibly.
> Related topic - code updates on live system. I've seen some problems with
> that too (I think the stored blocks in squeak don't use the new/changed
Yeah, you would have that problem alright. The blocks are storing the
context where they were created including variable bindings, position in
the executing code, etc. The code of the block is also defined in the
method. Once you recompile the method, the block may have different
code, the variables it's referring to are quite likely different, etc.
You'd encounter the same problem if a process was currently executing
inside a method when you recompiled it: that process would obviously
keep running through the old method; it can't switch to the new version
of the method midway through.
You can see this if you change the #go method of a task while party way
through the task. The old task code will continue to be used until you
enter it from the beginning again.
I personally consider loading code into the live system in use a little
risky at this point. A user could make a request while the new code is
half-loaded, for example (we don't have atomic fileins). You're also
completly exposed to something going wrong during filein and making the
system unusable. At work, we build a new image, and then use our load
balancing system to bring the new image up for new users while allowing
existing sessions to run to completion in the old image.
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