"minit" point of view

martin f krafft madduck at debian.org
Sat Aug 27 00:38:37 UTC 2005

also sprach Erich Schubert <erich.schubert at gmail.com> [2005.08.27.0209 +0200]:
> You can do that, but only if the pid 1234 is your child, or if it
> was detached and you are init. AFAIK.

Yes. That's what I meant.

Or if init sends on SIGCHLD signals to another process.

> a -> b
> b -> c
> d -> c
> d -> a
> The system tries to start a and d. a enters grey state, waiting for b.
> d enters grey state, waiting for c. assume c goes up, while b takes
> some time.
> So d is unblocked by c, and now depends on a. But a is in grey, so it
> assumes a loop!

Yes, the issue gets a whole lot more complicated with parallel
execution. FWIW, I think you only need to keep track of grey state
per execution thread. You don't need to track which service
requested which other service.

> Note that this information is useful for rollbacks, too.

I am not quite sure I picked up what rollbacks are.

> >   - Why would I depend on just any web server? I will depend on the
> >     web server which I have configured.
> Virtual services include cases where the provider is not known.
> Assuming you have a local web search engine installed, you'll want it
> to depend on your local webserver. You don't want to have to edit this
> dependency when you switch from apache to apache2 - the dependency
> should be just "web-server".

I disagree. If the web search was configured for apache, installing
roxen will break it. apache/apache2 is a special case because they
are related.

> >   - Why would I depend on a database server? MySQL and
> >   PostgreSQL are not compatible.
> Still your app might be able to use both. It might even be able to
> use both at the same time, doing like, a data transfer or
> comparison.

I have yet to see an application that selects whichever one is
available at run-time, or which can use both. If an application is
written for MySQL, it usually means the programmers have fairly low
clue levels (with few exceptions). If MySQL is later added, it can
usually not provide the whole feature set, or over time one database
support codebase grows out of date.

Really, is there a single application that can interchange PSQL and
MySQL? Such that if PSQL comes up faster and MySQL is installed,
installing PSQL is not going to break things?

> Speed reasons. I just want it to be started, but I don't
> immedeately need it. Like postfix - you might want it to depend on
> your dns service, but they can easily start at the same time.

So what happens when the DNS service fails to start?

 .''`.     martin f. krafft <madduck at debian.org>
: :'  :    proud Debian developer and author: http://debiansystem.info
`. `'`
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