Re: cache not up to date

On Jun 18, 17:58, Luka Frelih wrote:
> Subject: Re: cache not up to date
> > >I use Squid beta17 on a DEC OSF machine. Our old cache is a CERN
> > >3.0 on anothe
> > Note, there is no "Expires" or "Last-Modified" line. Without those,
> > Squid chooses a default TTL, maybe one week. If you want this page
>
> Does anybody know how CERN cache manages to deliver updated
> content? Does it use HEAD queries or some other conditional GET
> mechanism on the server? And of course, how this affects its
> performance against the squid cache?

Yes. During the last year, we've been running CERN, Netscape, and Squid
caches...

CERN *always* checked with the original host using if-modified-since
requests. There was no such thing as time-to-live. Consequently,
performance was awful on slow links and heavily loaded proxies, even if
the files were actually in the cache. With a Sparc 20 with 128MB main
memory, maximum reasonable load was about 20.000 requests per day.

Netscape worked pretty much like Squid, except it didn't use neighbors (if
you have a large cache, that doesn't give you a large performance penalty
-- yet;->), and it handled updates doing if-modified-since plus other
nifty features. It ran nicely on the Sparc 20 up to a little more than
100.000 requests per day; at 150.000 rpd, the machine spent 99% of the CPU
time doing context switches, paging and swapping, making local accesses as
slow as accesses to Brazil, say. If network problems blocked off a
popular part of the net, the system load would sky-rocket immediately,
heavily affecting access to the rest of the net, too. So, we had to
switch.

With Squid, we're now running close to maximum system load on the Sparc 20
at about 250.000 requests per day. With more memory (256MB) and the full
8GB of cache plus full if-modified-since updating, I'm hoping that we'll
be comfortable with Squid on that machine for another couple of months, up
to 400.000 rpd, say.
>
> L
>
>-- End of excerpt from Luka Frelih

Andreas

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