md5 collision

karlseguin nginx-forum at
Thu Sep 13 11:07:09 UTC 2012

Looking for help with a high number of md5 collisions with proxy caching.
It's my understanding that we shouldn't be getting any, but we seem to be
getting quite a few.

nginx version: nginx/1.2.3
built by gcc 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) 
configure arguments: --prefix=/opt/nginx --with-http_stub_status_module
--with-pcre=../pcre-8.31 --without-http_access_module
--without-http_auth_basic_module --without-http_autoindex_module
--without-http_browser_module --without-http_charset_module
--without-http_fastcgi_module --without-http_geo_module
--without-http_memcached_module --without-http_referer_module
--without-http_scgi_module --without-http_split_clients_module
--without-http_ssi_module --without-http_upstream_ip_hash_module
--without-http_userid_module --without-http_uwsgi_module
--conf-path=nginx.conf --error-log-path=/var/log/nginx/error.log
--http-log-path=/var/log/nginx/access.log --with-debug

I believe this might be relevant as well:

checking for system md library ... not found
checking for system md5 library ... not found
checking for OpenSSL md5 crypto library ... found
checking for zlib library ... found
creating objs/Makefile

Configuration summary
  + using PCRE library: ../pcre-8.31
  + OpenSSL library is not used
  + md5: using system crypto library
  + sha1 library is not used
  + using system zlib library

We are using the default cace key, though I've tried a few variations.  We
are doing one "weird" thing...The upstream server might re-request a
slightly modified version from Nginx in the hopes that this modified version
is in the cache. If it isn't, this modified request goes back to the
upstream, which then returns a file (which then goes back to the upstream to
fulfill the original request). At most, this is 2 loops... NGINX -->
Upstream --> NGINX --> Upstream   but the URLs wil be different between the
first set and the second one. Not sure that this is a problem, but since
it's the only odd thing, I figured I'd mention it.


Posted at Nginx Forum:,230686,230686#msg-230686

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