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Date: Mon, 14 Apr 2014 14:49:21 +0200
From: Maciej Bogucki <macbogucki@gmail.com>
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Subject: Re: mod_cache thundering herd bug
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>
>> 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.
>
> covener, mrumph, and I looked at this today at ApacheCon. I updated the bug with some comments
> and attached this patch.
>
>https://issues.apache.org/bugzilla/show_bug.cgi?id=50317

Hello,

Thank You very much for the patch but*it doesn't works*. When I'm doing ab (/usr/bin/ab -k -c 5 -n 10http://host/url) test the application get more than one request

1.1.1.1 - - [14/Apr/2014:14:01:58 +0200] "GET /url HTTP/1.0" 200 42398 9A68DBA96CED90DC517F7D6302F5A748.gpi-app1 1163 1163
1.1.1.1 - - [14/Apr/2014:14:02:05 +0200] "GET /url HTTP/1.0" 200 42398 D378685BBD4FB87C63A3A867ABFAFB3E.gpi-app1 2931 2930
1.1.1.1 - - [14/Apr/2014:14:02:05 +0200] "GET /url HTTP/1.0" 200 42398 8B77A0C68FC6F16E0BA3A89C7A614E1A.gpi-app1 2992 2991
1.1.1.1 - - [14/Apr/2014:14:02:05 +0200] "GET /url HTTP/1.0" 200 42398 57A48B49FB6C52E28F1FA97DDFCDC0C8.gpi-app1 3007 3006
1.1.1.1 - - [14/Apr/2014:14:02:05 +0200] "GET /url HTTP/1.0" 200 42398 71573080388181B3C55E88CB4BFAB890.gpi-app1 3051 3051
1.1.1.1 - - [14/Apr/2014:14:02:06 +0200] "GET /url HTTP/1.0" 200 42398 38DA8533D4F9B4046A2F607071652E94.gpi-app1 1412 1412


Here are more information how to reproduce it.

*Compilation*

cd /tmp
svn cohttp://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x
cd 2.2.x/
svn cohttp://svn.apache.org/repos/asf/apr/apr/branches/1.4.x  srclib/apr
svn cohttp://svn.apache.org/repos/asf/apr/apr-util/branches/1.4.x  srclib/apr-util
./buildconf
./configure --prefix=/etc/httpd --exec-prefix=/usr --bindir=/usr/bin
--sbindir=/usr/sbin --mandir=/usr/share/man --libdir=/usr/lib64
--sysconfdir=/etc/httpd/conf --includedir=/usr/include/httpd
--libexecdir=/usr/lib64/httpd/modules --datadir=/var/www
--with-installbuilddir=/usr/lib64/httpd/build --with-mpm=prefork
--with-apr=/usr --with-apr-util=/usr --enable-suexec --with-suexec
--with-suexec-caller=apache --with-suexec-docroot=/var/www
--with-suexec-logfile=/var/log/httpd/suexec.log
--with-suexec-bin=/usr/sbin/suexec --with-suexec-uidmin=500
--with-suexec-gidmin=100 --enable-pie --with-pcre
--enable-mods-shared=all --enable-ssl --with-ssl --enable-proxy
--enable-cache --enable-disk-cache --enable-ldap --enable-authnz-ldap
--enable-cgid --enable-authn-anon --enable-authn-alias
--disable-imagemap
patch -p0 < /root/rpmbuild/SOURCES/httpd-2.2.x-thunder.patch
make
make install

*Configuration**
*
<VirtualHost host:80>
     ...
     ...
     ## Cache
     CacheRoot /tmp/cache
     CacheEnable disk /
     CacheDisable /static/
     CacheMinFileSize 0
     CacheMaxFileSize 1048576
     CacheDirLevels 2
     CacheDirLength 2
     CacheLock on
     CacheLockPath /tmp/mod_cache-lock
     CacheLockMaxAge 5
     CacheIgnoreHeaders ETag Set-Cookie
     Header unset Expires
     Header unset Cache-Control
     Header always set Cache-Control "max-age=30,stale-while-revalidate=15"
</VirtualHost>

Best Regards
Maciej Bogucki