Expiration Behavior

Jehiah Czebotar jehiah at gmail.com
Mon May 7 18:39:40 UTC 2007

On 5/7/07, Gavin M. Roy <gmr at myyearbook.com> 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

I'm not sure what you mean when you say utilization is growing
disproportionately... but i can answer the second half of the question

memcached uses a lazy expiration, which means it uses no extra cpu
expiring items. When an item is requested (a get request) it checks
the expiration time to see if the item is still valid before returning
it to the client.

similarly when adding a new item to the cache, if the cache is full,
it will look at for expired items to replace before replacing the
least used items in the cache.


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