md5 fastcgi cache collisions

[Ian Evans]

On 25/09/2012 1:01 AM, Maxim Dounin wrote:
> I mean to ask about cache file, as reported in the error message
> provided.  But you may want to just provide several error messages
> to show variations possible.

2012/09/24 22:15:03 [crit] 641#0: *5061221 cache file 
"/var/lib/nginx/fastcgicache/3/04/41c3d443a1763965e630855f45c2b043" has 
md5 collision, client: x.x.x.x, server: www.example.com, request: "GET 
/cr/tomselleck/ HTTP/1.1", host: "www.example.com"
2012/09/24 22:41:52 [crit] 641#0: *5062571 cache file 
"/var/lib/nginx/fastcgicache/3/4d/c02f0ccb51ecff32ce8f8576384a54d3" has 
md5 collision, client: x.x.x.x, server: www.example.com, request: "GET 
/cr/katdennings/gallery HTTP/1.1", host: "www.example.com"
2012/09/24 22:53:31 [crit] 641#0: *5063073 cache file 
"/var/lib/nginx/fastcgicache/4/1f/3be079f5446cf74fbdcc64c6400301f4" has 
md5 collision, client: x.x.x.x, server: www.example.com, request: "GET 
/cr/drewbarrymore/ HTTP/1.1", host: "www.example.com"

> Fine - as a cache file, with binary header, "KEY: ..." line and so
> on?

No they appear to be clean text files...no binary stuff or KEY: line in 
them.

> You mean - md5 collision is reported on first request after you've
> removed the cache file?  Or on second request, when another cache
> file is already created by first request?

It was on the first request after I deleted it.

>
> What does nginx -V show?

nginx version: nginx/1.2.2
built by gcc 4.1.2 20080704 (Red Hat 4.1.2-52)
TLS SNI support disabled
configure arguments: --with-http_stub_status_module 
--with-http_ssl_module --with-debug --with-http_gzip_static_module 
--with-cc-opt='-I /usr/include' --with-ld-opt='-L /usr/lib'

>
> And could you please provide hd/xxd of several first bytes of a
> cache file, up to and including "KEY: " line?

As above, the fastcgi cache files are just plain html...is that wrong
>
> It would be also good to look at config and debug log of two
> requests after the cache file removal.

Right now, like a watched kettle that doesn't boil it's not happening as 
I type this email...but it has happened in the last hour.