Image Caching, when to update?

Sean Gillies sgillies at FRII.COM
Thu Aug 4 15:59:30 EDT 2005

On Aug 4, 2005, at 9:00 AM, Arnulf Christl wrote:

> Kyle Mulka wrote:
> [...]
>> I looked into squid and realized that thing it needs to know is when
>> the content changes so that it can refresh the cache. From what I've
>> heard so far, it doesn't sound like mapserver has any clue as to
>> when the map it serves might change. It seems that it would be
>> pretty easy for mapserver to simply determine if a map would change
>> based on the timestamp on the shapefiles its serving and either
>> the timestamp or the content of the map file.
> Kyle Mulka wrote:
>> Would it be good to move this discussion to mapserver-dev?
> Hmmm, i'd say leave them out front, they got enough on their hands 
> doing
> a great job serving maps (not that i would repeat myself... :-)
>>> By the looks of what i have seen in your demo you do a great job 
>>> already.
>> :-)
>> I'm using the PEAR Cache_Lite package for PHP right now. Its simple 
>> to use.
>> Only takes about 10 lines of code.
> [...]
>> Exactly. This is why we need at least something in mapserver that 
>> knows
>> about caching. Mapserver doesn't actually have to do the caching, but 
>> should
>> know when caching would be appropriate.
> I don't think any WMS service really knows a lot about what kind or
> actuality of data it actually serves (someone enlighten us?).
> Wouldn't this be something that metadata could be used for? Not that
> anybody would care to provide for good metadata...
> There are not too many thoughts about misusing metadata for this kind 
> of
> job as far as i know but basically it would fit in nicely?! This said 
> we
> might haul this discussion over to the OpenSDI clan instead of bullying
> the mapserver dev guys, but maybe we should just let them decide for
> themselves.
> Best,

IMO, MapServer should remain focussed on rendering map images, and 
caching should be left to other specialized applications or modules. 
This is the way the web works. See

for arguments why, from a smarter and better writer than myself.


Sean Gillies
sgillies at frii dot com

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