key collisions

Steven Grimm sgrimm at
Thu Feb 15 05:40:39 UTC 2007

A previous email on this topic had what seems like the most likely 
explanation to me: you are using connections that persist across script 
runs (nothing wrong with that inherently) and aborting before reading an 
entire response. The next script comes along, sends its request, and 
reads the remainder of the response from the previous script.

If you're aborting your scripts during the middle of reading a response 
-- and note that it wouldn't necessarily *your* code doing this; it 
could be aborted by the Python interpreter if you run out of memory, for 
example -- then you need to close the memcached connections to guarantee 
you don't have any stale data sitting around.


mark wrote:
> Hi Dave,
> I have not made much progress! I had the same problem of not being
> able to reproduce in the test environment! But in production I
> consistently get the problem!
> So I moved to cmemcached
> which is a python wrapper for the libmemcache. It seemed to solve the
> problem at the beginning, but what was happening was if there was a
> collision the app died with this message:
> [FATAL at 1170222010.740685] mcm_fetch_cmd():1176: memcache(4) protocol
> error: server sent data for key not in request
> I have not fixed this problem yet! It seems to be the same problem as
> before but the client here checking for consistency I think.
> It will be great if someone can find a fix for this!
> thanks
> mark
> On 2/14/07, Dave St.Germain <dcs at> wrote:
>> hi, mark,
>> I'm having the same problem with key collisions with the python
>> binding, and I was wondering if you've made any progress.  I haven't
>> been able to reproduce the problem in a test, but in production,
>> we'll encounter the problem all of a sudden after a while (the only
>> "solution" so far is to restart memcached).  The server returns the
>> wrong value for the requested key.  Not only that, but if you try a
>> get_many for key 'foo', you may get a response that has key 'bar' and
>> its value.
>> Since I haven't been able to reproduce this behavior in a test, I
>> don't yet know if it's the python binding or memcached itself.
>> Does anyone have any ideas?
>> Dave
>> > Hi
>> > I am consistently getting key collisions. There are total of around
>> > 2000 key
>> > value pairs cached.
>> > This is how I prepare the key for memcached:
>> > () where
>> > key is the unique
>> > id for the database row that I want to cache.
>> > When I do a 'get' for a specific key, I get a value of a different
>> > key.
>> > I am using python-memcached as the client.
>> > This is causing lot of problems. If anyone has faced similar issues
>> > or has
>> > any suggestions do reply.
>> > cheers
>> > mark

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