Re: [Gnu-arch-users] Re: Arch Cache & cached archives

[Aaron Bentley]

Stefan Monnier wrote:
> > I think that caching vs. memoizing should (at least ultimately) be a
> > finely tunable parameter.
>
> Could someone explain to me what is the difference between caching and
> memoizing here?

Roughly speaking, when you have a function or process that is costly to 
perform, and will likely be repeated, you can speed things up by storing 
the answer, and using that answer instead of repeating the process. 
This only works if the answer will always be the same for the same 
inputs, and usually requires a set of answers to be stored, indexed by 
the inputs that produced them.

With caching, in contrast, you are storing answers that may change. 
Caches usually have built-in expiration mechanisms, and ways to check 
whether the cached data is out of date.

To bring it back to tla, the tree state of a revision that exists is 
fixed and permanent.  Use any mirror of address@hidden, do "tla get 
address@hidden/tla--devo--1.3--patch-5", and you'll get equivalent 
results.

Cacherevs aren't permanent-- they can be added or removed at any time. 
So you may get different results running "tla cachedrevs" today versus 
running it tomorrow, even if you're using the same mirror.

So we can store a tarred, gzipped tree of a revision permanently.  But 
the information about which cacherevs a mirror contains is subject to 
change without notice.

Aaron