Mongrel users - Jan 2007 - Recommendation: Stalled Mongrel? Memcache Hates Spaces

Hi Everyone,

There''s quite a few of you who have contacted me about Mongrel suddenly
stopping.  After a lot of investigation, I found that the common thread between
all of you is memcache and Eric Hodel''s memcache-client.  People who
were running this combination would have intermittent pauses and investigating
the stalled mongrels showed that memcache-client was waiting for information
from memcached.

A friend just told me that he found out the problem is memcache does not accept
keys with spaces in them.  From this spec:

http://cvs.danga.com/browse.cgi/wcmtools/memcached/doc/protocol.txt?rev=HEAD

We have this paragraph:

"Data stored by memcached is identified with the help of a key. A key
is a text string which should uniquely identify the data for clients
that are interested in storing and retrieving it.  Currently the
length limit of a key is set at 250 characters (of course, normally
clients wouldn''t need to use such long keys); the key must not include
control characters or whitespace."

Notice the last part "the key most not include control characters or
whitespace".

Since memcache-client doesn''t currently escape your keys for you (not
sure if it should actually), you have to do this yourself or bad super evil
things happen.  The few people who have made this change report no more stopped
mongrel processes.

Please try this out and report back to me if it fixes things.

-- 
Zed A. Shaw, MUDCRAP-CE Master Black Belt Sifu
http://www.zedshaw.com/
http://www.awprofessional.com/title/0321483502 -- The Mongrel Book
http://mongrel.rubyforge.org/
http://www.lingr.com/room/3yXhqKbfPy8 -- Come get help.

On Jan 2, 2007, at 10:41 AM, Zed A. Shaw wrote:
> Since memcache-client doesn''t currently escape your keys for you  
> (not sure if it should actually), you have to do this yourself or  
> bad super evil things happen.  The few people who have made this  
> change report no more stopped mongrel processes.
>
> Please try this out and report back to me if it fixes things.
Zed- I rolled out a patch on the JibJab cluster yesterday to address  
this and I haven''t had to go after any dogs with a rubber hose since,  
and beating bad dogs has been a regular task for a while now.

I have no idea where spaces or control characters could get into the  
keys, but I''m not the only monkey banging on a keyboard here so who  
knows.

In case anybody wants a painless way to handle this, I added the  
following to my overrides:

class MemCache
   protected

   def make_cache_key(key)
     key.gsub!(/[^\w:]/, ''_'')
     @namespace.nil? ? key.to_s : "#{@namespace}:#{key}"
   end
end