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From Graham Leggett <minf...@sharp.fm>
Subject Re: mod_cache: store_body() bites off more than it can chew
Date Mon, 13 Sep 2010 14:04:03 GMT
On 13 Sep 2010, at 1:14 PM, Paul Fee wrote:

> Retrieving bodies from the cache has a similar scalability issue.  The
> CACHE_OUT filter makes a single call to the provider's  
> recall_body().  The
> entire body must be placed in a single brigade which is sent along the
> filter chain with a single ap_pass_brigade() call.

This isn't a problem for the cache, as the cached content is passed as  
a single FILE bucket.

When an upstream filter reads from the file bucket, the bucket  
"morphs" into a RAM resident HEAP bucket, followed by a file bucket  
representing the rest of the file. As long as a filter deletes each  
(heap) bucket as it reads it, we don't have memory issues.

This is no different to the default handler serving a static file.

For special needs, an implementation can define it's own bucket types  
which behave specially when read.

Regards,
Graham
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