question about the LRU

Brian Moon brianm at dealnews.com
Thu Jan 3 17:47:04 UTC 2008


Did you set a ttl for the items?  How similar to your real data is this 
test?  It seems to be a very academic test and may not reflect your 
actual usage even if you did see the results you hoped for.  I would 
suggest easing into memcached, watching the hit/miss ratio with cacti or 
some other monitoring and then deciding if memcached is right for you.

I can tell you that the LRU works fine for me.  I have never had an 
issue with things going away when I was not expecting them to.  And as 
always, it is a cache, not a storage system.  Don't put stuff in there 
that can not be recreated easily.

Mathieu Viel wrote:
> Hi guys. I have a question about the cache structure.
> 
> I want to use memcached to store some frequently used data chuncks and 
> the idea is to always have in memcached the most frequent requested 
> data;  if  i insert some new data when the memory for memcached is fully 
> used, i want the least requested data to be replaced.
> 
> I noticed in the FAQ that the cache structure is an LRU so i thought 
> "great i'll have almost nothing to do to implement this!" but, in order 
> to make sure, i ran some tests and i am dissapointed about the results.
> 
> With a 1Mb memcached, i first set an item with "1_1_1" as key and "1" as 
> value; i then get the value of this item (which is working ^^) and then 
> set some new randoms items i will never retrieve in order to fill the 
> memory (i made sure the key value will never be "1_1_1" for these 
> items); i then get the value of my "1_1_1" item to check if it's still 
> there. This "simple" process is working fine but when the memory is 
> filled, after some time, i can't get the value of my "1_1_1" item 
> anymore :S
> 
> I tried to check in verbose mode (-vv) and i can't get any interesting 
> information about this "issue".
> 
> I thought that since i frequently get the value of this item, it would 
> not make it the LRU one so its would never be somehow erased. Am i 
> wrong? I know about the different slabs sizes but since i always set the 
> value to "1", i think all these items are in the same category.
> 
> Thanks for help!
> 
> -- 
> Vivi


-- 

Brian Moon
Senior Developer
------------------------------
When you care enough to spend the very least.
http://dealnews.com/



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