Re: do packages depend on lexical order or {daily,weekly,monthly} cron jobs?

[Ian Jackson <ijackson@chiark.greenend.org.uk>]

Marc Haber writes ("do packages depend on lexical order or {daily,weekly,monthly} cron jobs?"):
> I am wondering whether there are packages that actually do depend on
> that and how do find out short of unpacking the entire archive and
> inspecting the scripts.

My feeling is that this situation is
  - quite unlikely
  - very hard to analyse without trying it
  - easy to remediate by combining the two cron jobs into a single
     (perhaps wrapper) script
  - but there is no benefit for changing the rules, because:

> Do you people know about packages that have cron jobs that depend on
> execution order? Would it probably be a good idea to proactively put
> language into the Policy Manual Chapter 9.5 that scripts put into the
> /etc/cron.{daily,weekly,monthly} MUST NOT depend on any execution
> order and MUST be prepared to run in parallel?

"Does not depend on order" and "can be run in parallel" are not the
same.  I worry about additional concurrency.  Unlike ordering bugs,
concurrency bugs are hard to find by testing.  So running these
scripts in parallel is risky.

And, I think running cron.fooly scripts in parallel is a bad idea.
The objective is to run them "at some point", not to get it done as
soon as possible.  Running them in sequence will save electricity,
may save wear on components, and will reduce overall impact on other
uses of the same system.

Ian.

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