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From Eric Covener <cove...@gmail.com>
Subject Re: mod_cache thundering herd bug
Date Wed, 09 Apr 2014 20:46:20 GMT
r1023398 for 2.2:

  http://people.apache.org/~covener/patches/httpd-2.2.x-thunder.diff

The remove_url() prevents other threads from serving a stale cached
file during refresh of a slow response, but it's unnecessary to have a
separate path because the refresh has to deal with 200s already.  When
the remove_url was added, there as no thundering herd lock / no
ability to serve stale content while one guy was reloading.

On Tue, Apr 8, 2014 at 2:11 PM, Jim Riggs <apache-lists@riggs.me> wrote:
> https://issues.apache.org/bugzilla/show_bug.cgi?id=50317
>
> While we are at ApacheCon, I would love to address this nasty bug with someone familiar
with 2.2's mod_cache. Our sites were brought down a few times last year before we finally
tracked it down to being this particular bug. I am using a crude backport of the 2.3 patch
(r1023398) in 2.2. It works, but I don't know if it is correct.
>
> Can someone look at this one with me? We really need to get this fixed in 2.2, because
there is NO thundering herd protection at all as things stand right now.
>
> - Jim
>



-- 
Eric Covener
covener@gmail.com

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