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From Niklas Edmundsson <ni...@acc.umu.se>
Subject Re: [PATCH] mod_disk_cache background copy
Date Wed, 11 Oct 2006 09:09:45 GMT
On Wed, 11 Oct 2006, Graham Leggett wrote:

>> This patch implements copying a file in the background so the client 
>> initiating the caching can get the file delivered by read-while-caching 
>> instead of having to wait for the file to finish.
>
> Something that Joe Orton raised, and that I've been looking into in more 
> detail.
>
> The copy_body function currently only supports file buckets, which 
> specifically excludes buckets generated by say mod_proxy, or mod_cgi. From my 
> testing, for these non file buckets, the response is downloaded and cached 
> fully, then the client gets fed data. Initially I understood this as an 
> optimisation specific to files, assuming that file buckets were the only 
> buckets that could potentially exceed available RAM, but the case where non 
> file buckets are present is currently unhandled.

I don't have enough knowledge of httpd internals to be sure, but 
doesn't the data-generating types insert flush buckets in the stream 
to avoid this? That said, mod_disk_cache seems to be totally unaware 
of flush buckets so I'm either barking up the wrong tree, it's handled 
on a higher level or it isn't handled.

> In theory, the copy body should be able to read from any brigade, rather than 
> just a file brigade, in such a way that it doesn't try and load 4.7GB into 
> RAM at once for file buckets.

The original reason for copy_body() was to have something that could 
be used in a background thread, and the only thing I'm sure can be 
copied in the background is plain files. Everything else must be 
handled the "old" way.

> I am jetlagged right now and can't think straight any more today, will carry 
> on looking at this tomorrow :)

OK. I'll be away for a week or so and might lag quite a bit in 
replying to stuff.

/Nikke
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  Niklas Edmundsson, Admin @ {acc,hpc2n}.umu.se      |     nikke@acc.umu.se
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