nova team mailing list archive

[Joshua McKenty <jmckenty@xxxxxxxxx>]

The biggest issue is the interaction with signals and the python threading model. Multiprocess certainly works (see the nova use of process pool), but you're making your code simpler at the cost of more complex process supervision (which I don't object to in this case).

Signals come up in deployment a lot, how to roll out code changes, etc. If we fix live migration, this gets much easier. 

Sent from my iPhone

On 2010-08-04, at 5:05 AM, Justin Santa Barbara <justin@xxxxxxxxxxxx> wrote:

> Forgive a Python noob's question, but what's wrong with just using Python threads?  Why introduce multiple processes?
> 
> It seems that Eric's benchmarks indicate that the overhead would be tolerable, and the code would definitely be much cleaner.
> 
> The multiple process idea is another argument in favor of simple threading... if we figure out sharding, we could run multiple compute service processes to get around scaling limits that going with simple threading might introduce (e.g. GIL contention).
> 
> Justin
> 
> 
> 
> On Tue, Aug 3, 2010 at 7:56 PM, Vishvananda Ishaya <vishvananda@xxxxxxxxx> wrote:
> If we want to go with the simplest possible approach, we could make the compute workers synchronous and just run multiple copies on each host.  We could make one of them 'read only' so it only answers simple/fast requests, and a few (4?) others for other long/io intensive tasks.  The ultimate would be to have each message actually have its own worker a la erlang, but that might be a bit extreme.
> 
> I've been doing a lot of the changes later that require switching everything to async.  It is a bit annoying to wrap your head around it, but it really isn't all that bad.  That said, I'm all for making things as simple as possible.
> 
> Vish
> 
> On Tue, Aug 3, 2010 at 6:30 PM, Justin Santa Barbara <justin@xxxxxxxxxxxx> wrote:
> Without meaning to make the twisted/eventlet flamewar any worse, can I just ask why we're not just using 'good old threads'?  I've asked Eric Day for his input based on his great benchmarks (http://oddments.org/?p=494).  My background is from the Java world, where threads work wonderfully - possibly even better than async: http://www.thebuzzmedia.com/java-io-faster-than-nio-old-is-new-again
> 
> I feel like Nova is greatly complicated by the async code, and I'm starting to see some of the pain of Twisted: it seems that _everything_ needs to be async in the long run, because if something calls a function that is (or could be) async, it must itself be async.  So yields and @defer.inlineCallbacks start cropping up everywhere.
> 
> One of the project goals seems to be simplicity of the code, for fewer bugs and to reduce barriers to entry, and it seems that if we could use 'plain old Python' that we would better achieve this goal than if we have to use an async framework.
> 
> I know that Python has its issues here with the GIL, but I'm just wondering whether, in the case of nova, threads might be good enough, and produce much easier to understand code?  I'm guessing that maybe the project started with threads - what happened?
> 
> Justin
> 
> 
> 
> _______________________________________________
> Mailing list: https://launchpad.net/~nova
> Post to     : nova@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~nova
> More help   : https://help.launchpad.net/ListHelp
> 
> 
> 
> _______________________________________________
> Mailing list: https://launchpad.net/~nova
> Post to     : nova@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~nova
> More help   : https://help.launchpad.net/ListHelp