Web-based Application in Revolution

Andre Garzia andre at andregarzia.com
Sun Oct 7 18:43:35 EDT 2007

Hello Thorsten and Ruslan,

thanks for the quick and detailed reply. The question was a rethorical one,
I am not building a web app like that, I just wanted to know what would
happen if someone did. The original poster was planning to use Valentina for
web apps with revolution, so I wanted to know what would happen if two
engine instances tried to access the same database.

I usually try to make web services so that my cgis poll for the service for
its query needs, or I simply use postgreSQL.

Again, I always learn more from such nice replies, even as I agree with you
guys from the start. I think Valentina Server is a very nice tool and as
soon as we can use it effectivily from Rev cgi apps it will be a major tool
for us.



On 10/7/07, Thorsten Hohage <thohage at objectmanufactur.com> wrote:
> Hi Andre,
> obviously I'm not Ruslan, but I build web-apps for over 10 years and
> I used Valentina in many apps.
> On 2007-10-07, at 22:07, Andre Garzia wrote:
> > usually when building Revolution web aps, people use apache cgi
> > interface,
> > so for each web request, apache will launch an instance of the
> > revolution
> > engine. If you have two concurrent requests, you will have two
> > instances
> > running.
> Yes, this is the common way for most of the dev-environments and for
> "small" solutions. If you really expect high number of concurrent
> users you perhaps should think about using a "real" web-application
> server.
> > Each with their own V4REV external loaded. What happens if they
> > both try to access the same Valentina database.
> Nothing good.
> > SQLite have built in methods for locking the file if they are
> > opened by more
> > than one application at the same time, so all transactions are
> > atomic. You
> > still have the problem of one instance overwritting the changes of
> > the other
> > instances, but you can guarantee that both accessess will happen
> > and will go
> > thru without file corruption.
> SQLLite with the given standard set of functions is only able to be
> opened from one client. There are some extensions trying to go around
> this, but the common "lock" is a full file lock of the db-file.
> So using any extension to go around it and looking at you scenario,
> what happened if you need a "real" transaction? Then there is nothing
> atomic left. Or what happened if an unexpected complex operation took
> several minutes, should all the other users wait?
> > What I am to say is that using SQLite you can build a minimal web
> > application if you're clever enough to build a locking mechanism to
> > prevent
> > overwritting other users changes.
> But then you could do the same with V4Rev. Build a file locking
> mechanism (or use on WIndows the system mechanism) for the used db-
> files and use V4Rev. But I didn't know any real world web app that's
> usable with such a mechanism in background.
> > Now, since I really like Valentina, can we do something similar
> > with V4REV,
> > can more than one application access the same database file without
> > using
> > Valentina Server?
> If you're talking about a "server" appm then I'm afraid you should
> use a db-server, in this case the VServer. There are several more
> advantages, then only have parallel access for several web-sessions.
> IMHO the most important word is CACHE! Using a file based DB solution
> with a file locking scenario the db is loaded again and again for
> every web-request! For most "real" db's this would be ways longer
> then the web-request will need to be executed. So each web-request
> will lock the db for even longer time and even less web-request are
> possible per second.
> Using a VServer the requested data is loaded into the cache, given
> you set a propitiate size, and all other reqeust are answered from
> cache, THIS is real speed improvement for a web app. When you now
> start using a db server you can use several more common patterns,
> i.e. store session information inside the db and only handle a id in
> the cookie.
> There is only one known exception. When you think of a CMS then you
> can set the Valentina-DB to read only and THEN you can open this db
> with several V4REV sessions at the same time.
> HTH,
> regards
> Thorsten Hohage
> --
> objectmanufactur.com - Hamburg,Germany
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