Re: Cache-DIGEST false hits

Hi, all,

Previously, I have reported about very high level of false CACHE_DIGEST_HITs

Alex Rousskov writes:

> Here is what you can try. Grep the logs for a recent false hit due to
> Cache Digest selection algorithm and then (assuming sibling A got a false hit
> from sibling B):
>
> 1) purge the object from A using client program
> 2) request the same object from A using client program
> 3) check that the object indeed came from B (X-Cache)
> 4) check that the object is indeed a false hit (X-Cache says MISS)
> 5) look at X-Cache-Lookup headers in the reply
> X-Cache-Lookup keeps the result of a store table lookup
> on B _before_ refresh-causing rules are checked:
>
Unfortunately, current version of client program doesn't support purge,
and I don't know how to delete object from cache.

I have studied log files since today midnight and found that all false
CACHE_DIGEST_HITs resulst from URLs containing cgi-bin, .cgi, ? , and
from some hosts like ad.doubleclick.net, counter.rambler.ru,
www.asiannet.com and www.mirabilis.com.

I have repeated to request objects from the last host (www.mirabilis.com)
using client program without and with -r option and had the same result:
every time cache-server A (www-cache.chg.ru) detects MISS and finds it in
digest of server B (proxy.itp.ac.ru). Resulting reply looks like this:

HTTP/1.0 200 OK
Date: Fri, 21 Aug 1998 05:07:35 GMT
Server: Apache/1.3.0 (Unix)
Content-Type: text/html
X-Cache: MISS from proxy.itp.ac.ru
X-Cache-Lookup: HIT from proxy.itp.ac.ru:3128
Age: 16670
X-Cache: MISS from www-cache.chg.ru
X-Cache-Lookup: HIT from www-cache.chg.ru:3128
Proxy-Connection: close

Both servers have the same refresh rules.

Serge.
Received on Fri Aug 21 1998 - 02:53:33 MDT