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From Mitch Gitman <mgit...@gmail.com>
Subject Re: caching strategies--is there room for a new one?
Date Tue, 08 Sep 2009 23:43:30 GMT
Steve, thanks for getting back.

I really don't want to go down that rabbit hole of debating
prolific/promiscuous versioning vs. snapshot versioning. Let's assume I've
made the choice to use so-called snapshot versioning, where the CI server
keeps overwriting integration versions when it does an ivy:publish. I can
see three ways to implement that approach which affect caching:
* Have a special integration repository and put checkmodified="true" on the
resolver for that repository. (Forgive me for mistakenly writing
lastmodified in previous posts.)
* Use a naming convention like "-SNAPSHOT" for your integration versions and
on the resolver specify a combination of checkmodified="true" and a
changingPattern.
* Override caching on a per-module basis using changing="true".

While I would say that the support for changing="true" could be made easier,
even then I wouldn't want to go with it. Just too high-maintenance. Same for
a naming convention like "-SNAPSHOT". That leaves only the first approach:
integration repository + checkmodified="true".

While I think having an integration repository is a good idea in its own
right, I hate for it to be the only way to do snapshot versioning that
doesn't have hidden landmines. One of the things I like about Ivy is that it
offers you different ways to accomplish something. One thing I don't like is
that--fortunately, only on rare occasion--when you get right down to it,
there's really only one way that works and isn't a pain in the butt, and all
the other approaches, while available, are really deprecated.

Now you could try to make the hard options--changing="true" and
changingPattern--a little easier. But they'll still be hard options. What
I'd like is just to have another easy option in the mix. My proposal is put
another filter on checkmodified="true"--where it only checks for a given
status or lower. This way you don't have to set up a special integration
repository from the outset just to avoid running into insidious, mysterious
bugs that eventually trace their way back to over-caching.

On Tue, Sep 8, 2009 at 11:07 AM, Stephen Nesbitt <
stephen_nesbitt@alumni.cmc.edu> wrote:

> Mitch:
>
> I guess I'm not completely clear on what problem you are trying to solve
> here.
> Is it to make using the "changing" attribute easier?
>
> From a configuration management perspective, I consider any need for a
> "changing" flag to be poor (or at least not ideal) practice - it's
> essentially
> an admission that I don't know what I've got and that I have failed to
> uniquely identify my artifacts.
>
> I suspect this has something to do with the convention of tagging artifacts
> with -SNAPSHOT or something and avoidance of promiscuous versioning. If so,
> what I would really like to know is what is the issue with promiscuous
> versioning and what problem does tagging everything with -SNAPSHOT provide?
>
> I have a sneaking suspicion that the "changing" attribute is really a hack
> to
> cover a problem in repository management.
>
> -steve
>
> Stephen Nesbitt
> Absaroka Tech
> Build and Configuration Management Consulting
> steve.nesbitt@absaroka-tech.com
>
> On Sunday 30 August 2009 08:16:16 pm Mitch Gitman wrote:
> > Carlton's question came at a time when I was pondering the caching
> > strategies Ivy implicitly offers. I can identify four:
> >
> >    1. Always trust the cache.
> >    2. For a given resolver, never trust the cache, i.e.
> lastmodified="true"
> >  by itself. This makes sense if you can split your repositories into
> >  integration and release repositories. Trust cache for release; distrust
> >  cache for integration.
> >    3. For a given resolver, only distrust the cache when the revision
> value
> >    meets a specified changing pattern. This makes sense if you don't have
> a
> >    separate integration repository but you don't mind going to the
> trouble
> >  of giving all your integration revisions the same naming pattern, like
> >  a–SNAPSHOT
> >    suffix.
> >    4. Check the repository on a per-dependency basis. This only makes
> sense
> >    if you don't want to use a separate integration repository or a
> special
> >    revision naming convention like –SNAPSHOT, but you can deal with the
> >    overhead of (A) remembering to manually specify changing="true" and
> then
> >    (B) remembering to turn it off when you're ready to do a release
> >  publish.
> >
> > Approach 4 is really high-precision, but it's just so high-maintenance
> and
> > error-prone. I wish there were a way with *ivy:deliver *or *ivy:publish
> *to
> > automatically turn off the changing mode, such as if you're publishing to
> > release status. I mean, it doesn't make sense for an Ivy module in
> release
> > status to be depending on other Ivy modules that could be changing out
> from
> > under it.
> >
> > Anyway, I can understand why approach 2, in combination with an
> integration
> > repository, is recommended.
> >
> > But I wonder if there's potentially a simpler approach where you don't
> even
> > need a separate integration repository. (I acknowledge having a separate
> > integration repository has value in its own right apart from caching.)
> > Consider these observations:
> >
> >    - Under normal caching situations, there's a high correlation between
> >  (A) your willingness to trust the cache for a given module and (B) that
> >  module's publication status. Milestone or release=trust cache.
> >  Integration=distrust cache.
> >    - There's a certain information redundancy in having an integration
> >    repository. All the modules published there have status="integration",
> >    but just the existence of the repository is saying the same.
> >    - Under normal circumstances, a module graduates from integration to
> >    milestone to release (using the default statuses). A module never goes
> >    backwards in status. That makes about as much sense as flunking from
> >  sixth grade down to fifth grade.
> >
> > So what if you could specify something like the following on a resolver?
> > checkmodified="true" maxcheckstatus="integration"
> >
> > What would this combination mean? For any given cached module, Ivy will
> go
> > out to the Ivy repository and compare the last modified timestamp only if
> > the cached ivy.xml has a status of integration or lower. Once Ivy
> downloads
> > a copy of that module that has a higher status, it subsequently stops
> > checking. But that's what you want.
> >
> > I can understand why folks wouldn't have use for such a feature if
> they're
> > already using an integration repository. But if Ivy's already
> > supporting changingPattern
> > and changing="true", you have to admit this is worlds simpler.
> >
> > Or is it? So what am I missing here?
> >
>

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