[Zope] Re: Accelerating images without proxy

[Oliver Bleutgen]

Maik Jablonski wrote:
> Marc Burgauer wrote:
> 
>> I have analysed the problem and I believe I could get a major boost if we
>> could just cache some images. There are about two dozen images, mainly 
>> logos
>> and navigation images that are used on almost every page. If I could just
>> cache these, that should help a lot.
>>
>> I looked into the various internal mechanisms (Accelerated HTTP Cache
>> Managers, Cache-tab on image object) and read the help. But I'm still not
>> sure if this is helpful. The help text constantly tells me that some
>> operations using cache can backfire and become more expensive.
>>
>> Can anybody share any light on this issue, please?
> 
> 
> You should use an Accelerated HTTP Cache Manager, which only caches your 
> images (see Tab: Associate -> Select "Image"). This will add some 
> additional headers to the image-responses which tell proxies on the way 
> or the clients browsers to cache the images for the specified time. All 
> your clients won't request the images anymore from the server which 
> should take some load from the server.

Images delivered by zope are quite extensively cached on the browser 
side per default, even without configuring something in zope.
I.e. zope sends appropriate "not modified" headers if it gets the right 
request from the browser (which nearly all browsers do). You can see 
this when grepping the logs for "304", or using a log analyzer. I just 
checked on two sites of us, and on one, which has many different images, 
I get 10% of all responses to be "304", while on the other, whose images 
consist mainly of navigation buttons, I get 50% of all images cached. 
This was btw. a big problem for us using localizer, because when 
switching languages because the images wouldn't change.

Since sending the 304 shouldn't be expensive, I doubt it will help much 
for the speed of the site, but esp. not if it is network I/O bound.

One thing which is important is to link the navigation images with their 
absolute url, not using acquisition, so that the browser will be able to 
see that the images are identical.

cheers,
oliver