Re: [dwm] Re: Crash-only software

[2009-02-03 22:33] Marcin Cieslak <saper_AT_system.pl>
>
> I don't like this approach. I have always preferred software that "fails
> fast". As soon as something is wrong - just abort with debugging information
> what went wrong.
>
> I see some issues with the approach described in the paper. It assumes that
> the state saved is okay - I think that crashes occur _because_ internal
> state is inconsistent or wrong.

Seems as if you got a different view on the concept than me. I think
its not so much about error handling in the first way, but about
organizing state so that killing a software is equal to shutting it
down.

> Sure, you can dump internal state regularly
> for recovery - but it's like with backups - you never know which one is
> really clean and okay until you try to restore.
>
> Software bugs will sometimes create incorrect data. This may go unnoticed
> for some longer time.

But if you implement a crash-only design, then these problems will get
erased. Exactly this is the sense of such a design: Have a software
that handles these problems in a _sane_ way. Also these situations
will be tested throughoutly as they are the _normal_ situations.

> I think that authors unnecessarily assume that software components are
> "black boxes" that need to be kept up at all costs. This is not the right
> approach for availability I think. Most issues will occur when the component
> is upgraded and needs to use/migrate old data or sometimes to cooperate with
> still not upgraded components. If something goes wrong, the rollback becomes
> the issue also - if I have new, badly-behaving components that dumped its
> state in a new format, how do I go back?

Of course, compatibility is an issue, but IMO an unrelated one.

> Sweeping problems under the carpet is not going to help much...

I think the crash-only approach explicitely wants to focus on the
problems, that means actually _not_ sweeping them under the carpet.

However, I know that I don't stick close to the paper. I base my
argumentation also a lot on thoughts I made, inspired by the paper.
Thus we might discuss from different points of view ...

meillo