[aida] 6.2 news: Image based persistency

Nicholas Moore nicholas.moore at tsr-i.com
Tue Feb 22 18:18:37 CET 2011


No doubt you would declare an interest here, Chris, having done stirling work in the creation of Magma. :-)

I toyed with the idea of using Magma for my blog, which has been live since 2007. In the end, for my size site it was just not worth the effort. I write out all new blogs to a file, and the hourly save that comes with Aida 6.2 is perfectly adequate for that and the other sites I maintain. I run two headless images for my six sites and they are very stable. I have never yet experienced any image corruption, so am not motivated to find solutions for such absent corruption.

As for upgrading an image, I have just upgraded from Aida 6.1 to 6.2 without any model issues.

Of course, my sites are each small, but then I suspect that many  Aida implementations will fall into that category, and for me, image based persistence works fine. Indeed I have always been attracted to the notion that a Smalltalk image is effectively and object-oriented database in ram, and would like to see that notion developed rather more than it has been.

Having said that, I like Magma and if I needed more traditional persistence would almost certainly go down the Magma path, except that I use VW on which Magma is not available.

Regards,

Nicholas

On Tuesday 22 Feb 2011 17:10:21 Chris Muller wrote:
> You forgot to mention, there is also Magma to "escape" for really big
> projects.  BTW, does Aida run on GemStone?
> 
> I don't want to start a debate, but I think it's good to be
> conservative about advocacy for image-persistence.  IMO, it's fine for
> "small prototypes" (< 1GB model) where it's ok to lose data, but not
> "medium" ones (2 - 10GB) and not any project where it's not ok to lose
> data.  If the image is somehow corrupted and being saved in that state
> so it won't relaunch, you would not discover this until the _next_time
> you tried to restart your server, which could be months later!  Sure,
> that scenario is unlikely, but certainly possible, and it would be a
> total loss if it happened which, to me, is unacceptable.
> 
> What happens if the model grows faster than expected beyond memory
> capacity?  How do you get your app ported over to GemStone w/
> licensing, etc. and back up and running quickly?  How does one
> "upgrade their image" if the model is stuck in an old image?  Does the
> image save start to take longer and longer as the image grows?
> 
> Magma is simple and fast enough that, if I ever had any qualms about
> any of the above issues, then I would just start with that in the
> first place, and be comforted in knowing I'm prepared for growth and
> cannot lose data.  No object-persistence mechanism for Squeak or Pharo
> comes close to Magma in terms of the _safety_ of the domain model.
> 
>  - Chris
> 
> 
> 2011/2/22 Janko Mivšek <janko.mivsek at eranova.si>:
> > Dear Aiders,
> >
> > In newest 6.2 one very important feature is enabled by default and it is
> > important to understand the consequences of that: Image based persistency.
> >
> > Image based persistency basically means a periodic snapshoot of the
> > image to the disk. This is the simplest but very effective persistency
> > solution which I'm successfully using on my production servers for
> > years. It is suitable for low to medium sized projects, in my experience
> > near 99% of all. And you have a Gemstone as a solution to "escape" for
> > really big projects.
> >
> > Aida 6.2 has a hourly snapshot enabled by default and active immediately
> > after the installation. It is active on OneClick image as well.
> >
> > Snapshot is implemented in method:
> >
> >        AIDASite class>>imageSnapshot.
> >
> > Snapshot is periodically scheduled in Aida's scheduler, see:
> >
> >        AIDASite default scheduler
> >
> > Another feature enabled by default is a nightly cleanup, which removes
> > all nonactive guest sessions and release application state on all
> > session. This feautre is also scheduled in above mentioned scheduler.
> >
> > Best regards
> > Janko
> >
> > --
> > Janko Mivšek
> > Aida/Web
> > Smalltalk Web Application Server
> > http://www.aidaweb.si
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> > Aida at aidaweb.si
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> >
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-- 
Nicholas Moore
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