On Thu, Oct 7, 2010 at 5:49 PM, Lars Marowsky-Bree <[email protected]> wrote:
> On 2010-10-05T18:03:17, Andrew Beekhof <[email protected]> wrote:
>
>> > Anyway, it's too late to change the semantics as
>> > that would change behaviour of the existing clusters.
>> Actually the solution is really quite easy.
>>
>> 1. Make constraints with > 2 elements and no/insufficient brackets
>> produce a warning and require user confirmation.
>> There is certainly precedent for things in the shell becoming warnings
>> that weren't previously.
>>
>> 2. Decide on two types of brackets to use, one for ordered and one for
>> unordered.
>
> Admittedly, I find the whole notion of "ordered" collocation extremely
> annoying, and unclean design. I'd much rather not have the shell support
> that at all.
>
> That collocation is expressed in what amounts to the reverse of the
> "natural" consequence of ordering is a bit confusing, but I'm afraid
> we're stuck with that now.
No, we're not.
>
>
> For order + colocation, a rather common combination of constraints, what
> I'd rather have the shell do is detect a match between them and merge
> them in the shell syntax - there's no reason why a shell statement
> _must_ only expand to a single XML element.
>
> So:
>
> order foo inf: a b
> colocation bar inf: b a
>
> would be merged to
>
> join foo: inf: a b
>
> in the shell. And then do the same for sets; it's not much more
> difficult, and we'll all be much cleaner off than with trying to
> remember what the heck [] () {} were about. And keep it at one set of
> parenthesis.
I don't see what one has to do with the other.
I'd be in favor of the join construct above (although I'd probably
call it "depends"), but it doesn't address the original problem that
the shell syntax for colocation constraints switches direction when
you add a third element[1].
Or do you imagine that no-one will ever use colocation constraints
ever again once "join" exists?
[1] Note that the XML syntax has no "direction" for colocation
constraints without sets.
> (Add an expand command to turn the automated merge of if people want to
> etc etc, but you get the idea.)
>
>
>
> Regards,
> Lars
>
> --
> Architect Storage/HA, OPS Engineering, Novell, Inc.
> SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
> "Experience is the name everyone gives to their mistakes." -- Oscar Wilde
>
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