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From Justin Erenkrantz <jus...@erenkrantz.com>
Subject Re: [PATCH] mod_disk_cache deterministic tempfiles
Date Wed, 17 Aug 2005 22:22:20 GMT
--On August 17, 2005 9:29:05 PM +0100 Colm MacCarthaigh <colm@stdlib.net> 
wrote:

> Why bother renaming the file for such an implementation? If a
> half-cached file can be served from, and this handled properly, the
> rename would no longer make any sense :)
>
> For a disk cache it would be tricky to discern between a cached file
> that is half there due to a sudden httpd exit, and a cached file that is
> half there because a proxy or CGI backend is blocking.

Exactly.  This is why I've avoided this functionality.  I don't think it 
can be implemented effectively or efficiently.

I absolutely dislike the idea of stalling a request because another 
worker/thread *might* be fetching it.  We should never purposely stall a 
request because another worker *might* have a request outstanding.

> One solution that avoids that may be to create random uuid at httpd
> start time, and store that in every cache object. That way the caching
> layer can determine if the half-cached file on disk belongs to a
> "current" instance of httpd - and we assume it's in-flight - or if it
> belongs to a previous instance of httpd, and we assume it's leftover
> from a sudden death.

It doesn't handle the case when a sibling died.  -- justin

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