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From "Graham Leggett" <minf...@sharp.fm>
Subject Re: mod_disk_cache patch, preview edition (was: new cache arch)
Date Tue, 02 May 2006 15:12:47 GMT
On Tue, May 2, 2006 3:50 pm, Niklas Edmundsson said:

> Are there partially cached files? If I request the last 200 bytes of a
> 4.3GB DVD image, the bucket brigade contains the complete file... The
> headers says ranges and all sorts of things but they don't match
> what's cached.

By "partially cached" I meant a file that was half cached, and other
processes/threads are serving content from that cache.

>> What may be useful is a cache header with some metadata in it giving the
>> total size and a "download failed" flag, which goes in front of the
>> headers. The metadata can also contain the offset of the body.
>
> I solved it with size in the body and a timeout mechanism, a "download
> failed" flag doesn't cope with segfaults.

True, but a timeout forces the end user to wait in cases where we already
know the backend is dead. This typically won't happen with a disk backend,
but it will happen with a mod_proxy backend (think connection reset by
peer).

> It's possible, but since I needed to hammer so hard at mod_disk_cache
> to get it in the shape I wanted it I set out to first get the whole
> thing working and then worry about breaking the patch into manageable
> pieces. For example, by doing it all-incremental there would have been
> a dozen or so disk format change-patches, and I really don't think you
> would have wanted that :)

We do want that if possible :) Small changes are easy to understand, and
thus in turn easy to get the three votes needed for inclusion into httpd
v2.2 from trunk.

Regards,
Graham
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