Caching wtf



  • I go to a website that has about two dozen small images. Something's wrong with the server and 3 or 4 don't show up. That's OK, I'll just F5 to refresh it. Now there are still 3 or 4 missing...but different ones this time. Every time I refresh, at least one is missing (because this web server is known for such problems)...but by this point shouldn't the cache have all of the images stored?

    I check the cache folder and sure enough it's happily taking up 25 mb of my drive. So wtf??? Yes I already know the real WTF is that I'm still using IE. Beat ya to it.



  • Well, aren't you going to give us the URL so we can DDOS test it ourselves?



  • Well pressing F5 to refresh always attempts to get all the content again, the difference is that items which are already cached use conditional gets, so if the item hasn't changed the response is a small "not modified" response. I would suspect that a failure would cause the cached item to be discarded.



  • The server may be sending one of the "no-cache" headers with the page or images (are you sure that 25MB includes those images?), or may simply be reporting the last modified date as either now, or in the future (and so IE would think that it needs to refetch the images).



  • @Juifeng said:

    I saw this happen in firefox, using the fasterfox extension. Fasterfox opens multiple connections (at the same time) to the web server to retrieve images, style sheets, and so on. The server limited max. connections per ip, and fasterfox exceeded that limit. Then i decided to stop using fasterfox.

    Two weeks later i switched to opera. I dont know if its using more than 5 connections at the same time, but i dont hope so. ;P



    A proper web server would queue requests that it has received beyond it's max xonnections and send a reply after other connections have closed.  What the hell web server was it?



  • @tster said:

    @Juifeng said:
    I saw this happen in firefox, using the fasterfox extension. Fasterfox opens multiple connections (at the same time) to the web server to retrieve images, style sheets, and so on. The server limited max. connections per ip, and fasterfox exceeded that limit. Then i decided to stop using fasterfox.

    Two weeks later i switched to opera. I dont know if its using more than 5 connections at the same time, but i dont hope so. ;P



    A proper web server would queue requests that it has received beyond it's max xonnections and send a reply after other connections have closed.  What the hell web server was it?


    IIS on Windows 2k Professional has a concurrent connection limit that's pretty low (5 or 10, I think). It will drop requests after it hits the limit. I've seen that cause behavior very similar to what's described.


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