[aida] 6.2 news: Image based persistency

Chris Muller asqueaker at gmail.com
Tue Feb 22 17:10:21 CET 2011


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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