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From Berin Loritsch <blorit...@apache.org>
Subject Re: Caching and key collision?
Date Tue, 15 Jan 2002 17:31:18 GMT
Kuhnle@heinrich-partner.de wrote:

> 
> Hi,
> 
> I noticed caching is done by generating a key with generateKey. This 
> returns a long, which is commonly generated through hashing. The 
> documentation says "This key must be unique inside the space of this 
> component", which hashing does not guarantee. Won't this lead the cache 
> to confusing two different cacheable objects (files/server pages/etc.) 
> which accidently have the same cache value? This sure is an unlikely 
> event, but ist still can happen. Also, on pipelines with many program 
> steps, the cache generates very long file names some operatings systems 
> can't cope with.


Regarding the last issue, I have been a victim of that.  Windows 9x
cannot handle the long filenames generated by the cache.

However, Windows NT and just about every Unix can, so to me this is a
minor issue--who in their right mind would want to serve anything from
Windows?


A more fundamental issue however is in regards to how quickly an OS

is on seeks.  Windows favors shallow directories and large numbers of files
in a directory.  UNIX favors deep directories and small numbers of files
in a directory.

When you go to the extreme that each does not like, you *really* notice
the slowness.  I have had my Windows machine block for 15 seconds at a
time while navigating very deep hierarchies (this is especially true on
Win 9x).  Again, while working on a Perl webapp that cached info on the
drive, Linux would pause for a few seconds (5-6) when there were about
1000 entries in a directory before displaying the contents of the directory.

If we could tune our cache to favor what the OS favors, it would add
just that extra something to make the cache even faster.




-- 

"They that give up essential liberty to obtain a little temporary safety
  deserve neither liberty nor safety."
                 - Benjamin Franklin


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