Re: [squid-users] Cache size, how much is enough, how much is a waste?

From: Chris Tilbury <>
Date: Thu, 30 Jul 1998 09:44:22 +0100

On Wed, Jul 29, 1998 at 08:42:47PM -0400, B. Richardson wrote:

> Three days worth for me is I think around 10 GB (do not have a
> dedicated production server, still in the specing out and testing
> phase). Load is around 700k connections per day.
> Let me speculate here.
> Starting from empty, my hit ratio is going to increase until
> I accumulate 10 GB (or 3 days worth).
> After I hit 10 GB, it is still going to increase but more
> slowly till I get to around 24 GB.
> Above 24 GB, I will enter the area of diminishing returns.
> I can add a lot of disk space, but my hit ratio is going
> to improve only slightly.

You also need to factor into this the varying object sizes. What's the
maximum cached object size you have at the moment? What proportion of
objects are you retrieving for your clients which are not being cached
because they are too large? How repeated are these accesses?

Also, remember that in terms of bandwidth saving, the document hit rate is
less important than the hit rate expressed in terms of Kb. To increase the
former, you need to start caching larger objects, which need more disk

You also need to consider the effects of internet "hot spots" on usage
patterns. A good example here is to consider what happens when Netscape
release a new WWW browser.

What impact does this event on you: Do many users download it? If so, is the
object being cached, or is it too big and is it simply being deleted? To
what extent would you benefit from having enough space to store abnormally
large (when compared to the median size) files like this, which may only
achieve very high request rates for a short time period, but which generate
very large amounts of traffic over that period.

More disk generally means more objects, yes, but it can also mean _larger_
objects. Storing larger objects could increase the saving you make in
bandwidth terms much more significantly, albeit on a more "seasonal" basis
in many cases.

Just some thoughts, anyway.



Chris Tilbury, UNIX Systems Administrator, IT Services, University of Warwick
EMAIL: PHONE: +44 1203 523365(V)/+44 1203 523267(F)
Received on Thu Jul 30 1998 - 01:46:32 MDT

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