Re: ENTRY_SPECIAL => content pinning?

Hi Joe

> >
> > --- Joe Cooper <joe@swelltech.com> wrote:
>
> Right. The icons that Squid uses for FTP directory
> listings, etc. are
> loaded at startup, and I suppose they live in memory
> for the life of the
> process. It wouldn't make sense for them to swap
> out to disk, since we
> already have local copies of them.
>

Well, I just checked my cache directory and I see
these MIME icons images all there. I checked the
mimeLoadIconFile function and see that they are set to
ENTRY_SPECIAL *after* it calls storeAppend. So they
are actually SwapOutAble. I guess they are THE first
pinned objects in squid. ;-) BTW, someone else please
fix me if I say something wrong.

>
> Does pinning imply we should be controlling how long
> an item is fresh?
> I was thinking of pinning merely in terms of "These
> items, marked
> PINNED, are priority items, and should not be
> removed from the cache
> object store until they expire (expiry being set via
> normal mechanisms)."
>

My ex-boss asked me to do something similar to object
pinning. He wanted certain objects to stay in cache
and won't be evicted by removal policies. We ended up
writing something else to do this instead of modifying
squid.

As to how to get rid of these pinned objects later, he
wanted: 1) explicitly use a PURGE command (maybe thru
a client); and 2) after some time, it is unpinned and
becomes a normal object that is subjected to the
removal policies (kinda similar to expiration)

Cheers,
Yee Man

> Maybe I'm missing a useful aspect of what you're
> getting at, but from my
> understanding of the common uses for pinning an
> object into the cache,
> the purpose is to /prefer/ certain objects when
> deciding what to remove,
> not altering how long the object stays fresh. We
> can already alter how
> long an item stays fresh using refresh patterns (and
> we can enforce
> longer freshnesses for patterns using the reload
> into IMS options,
> etc.). I think all a cache_pinned directive needs
> to do is decide what
> gets pinned (and no matter how infrequently it is
> used, we keep it on
> disk). Right? Or do you have other uses in mind?
>

IMHO, people don't care about refreshing the object in
pinning. If they want to refresh, they will run a
PURGE and then pin an updated object. Maybe you can
post something on isp-caching and see what people
really want.

Cheers,
Yee Man

__________________________________________________
Do You Yahoo!?
Yahoo! - Official partner of 2002 FIFA World Cup
http://fifaworldcup.yahoo.com
Received on Sat May 25 2002 - 22:57:43 MDT