Feedback on Tag Support

dormando dormando at
Fri May 9 18:07:53 UTC 2008

On skimming the code it looks like tag invalidating loops over all items 
and removes them from a linked list, then removes the tag from the splay 


Jonathan Ariel wrote:
> It doesn't seems to be a loop, it says "We use hash and splay tree, make 
> the tag_add and tag_delete commands very quickly, and save memory as 
> much as possible."
> On Fri, May 9, 2008 at 2:44 PM, Dustin Sallings <dustin at 
> <mailto:dustin at>> wrote:
>     On May 9, 2008, at 9:52, John Kramlich wrote:
>>     Is anyone using the variant of memcached v 1.2.4 that supports
>>     tagging found at the following
>>     URL ?  I am in the planning
>>     stages of major feature additions to my web application and would
>>     really like to use this version.  I'm looking for feedback from
>>     others who have used it.  Is it stable enough for production use?
>>      Any issues?
>     I think tagging is a generally useful feature, but we honestly
>     haven't put a lot of effort into reviewing the tag code.
>     In particular, we want tagging to be cheap on both setting and
>     invalidating.  If either operation has to perform more than a single
>     lookup, then it may not be desirable.  In particular, deleting by
>     tag is a loop (within a lock and with another nested loop within
>     it), which may cause the server to hang for long periods of time
>     when invalidating a widely-used tag.  It *should* be possible to do
>     this without such a loop.
>     -- 
>     Dustin Sallings

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