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From Chris Bowditch <bowditch_ch...@hotmail.com>
Subject Re: Image Cache: behaviour for failed URIs
Date Thu, 26 Mar 2009 17:39:45 GMT
Jeremias Maerki wrote:

> I've been made aware that the current way failed URIs are handled in the
> image cache may not be ideal: If a URI is only temporarily unavailable,
> the image identified by this URI will remain invalid until the JVM is
> restarted or the cache is cleared explicitely.
> 
> The reason for the failed set is that FOP accesses an image twice for a
> single document (FO stage and rendering stage). For a slow connection,
> that would slow down the formatter quite a bit.
> 
> How about this? Each entry in the failure set gets a time stamp and a
> timeout will invalidate the entry, forcing a retry next time the URI is
> accessed. The timeout could be set to 0, which would effectively disable
> that failed set. A value > 0 would set the timeout to n seconds. And a
> negative value equals to infinity which would represent the current
> behaviour.

I like this proposal, so +1.

Just to provide some context, imagine you are batch processing 1000 
documents and they all use the same image. If the images are served by a 
remote servlet and a network glitch causes the 500th document to fail to 
retrieve the image then documents 501-1000 will all fail. Really only 
document 500 should fail.

Providing such a configuration setting lets the user decide whether to 
scarifice performance in favour of robustness.

> 
> If nobody sees a problem with that I'll implement that shortly.

Thanks,

Chris




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