Expiration Behavior

Jason Edgecombe jason at rampaginggeek.com
Mon May 7 20:32:12 UTC 2007

If the cache is full with non-expired items, then an add will push out 
the least-recently-used item.*

* actually it the LRU item in the slab.


Gavin M. Roy wrote:
> Thanks, I assume since I don't see any walk type of functionality in 
> the API, that there's no real way to find out truly how much space one 
> has free after the memcache is full with expired content.  What will 
> happen once the cache is full with non-expired content and an add is 
> called?  Is the only real way to test for free-space in the memcached 
> to look for errors in reponse to an add, or am I missing something?
> Gavin
> On 5/7/07, *Jason Edgecombe* <jason at rampaginggeek.com 
> <mailto:jason at rampaginggeek.com>> wrote:
>     Gavin M. Roy wrote:
>     > Hello,
>     >
>     > Am running memcached in production on a fairly large site and am
>     > noticing that while I'm putting in expirations, the size of the
>     > utilization is growing disproportionately with the expected
>     growth of
>     > the cache based upon what we implemented it for.  By some
>     testing, it
>     > seems that items that are expired from the cache are only
>     removed when
>     > the get request is sent.  Is our interpretation of this behavior
>     > correct, or does content in the cache expire based upon the
>     timestamp
>     > through some internal stack?  If it's the later how often does the
>     > daemon run through to get rid of expired content?
>     >
>     > TIA,
>     >
>     > Gavin
>     Hi Gavin,
>     That is correct. expired items are only purged when a get request is
>     sent for the expired item or the expired item is cleared because the
>     storage is needed.
>     Jason

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