garbage collector

[Timo Ewalds]

You might want to try a patch I posted several months ago instead of an 
external garbage collector.

http://lists.danga.com/pipermail/memcached/2007-August/005034.html

Timo

Ivan Szanto wrote:
> Hi,
>
> we wrote an external garbage collector for memcached and it works fine.
> We would like to make it available as an open source software. Is this 
> interesting to the members of this list?
> Please let me know where we can post it.
>
> The story:
>
> We apply memcached to cache all kinds of items of a largish website 
> written in php.
> We found it's working great!
>
> But after a couple of days of usage we began to have problems. These 
> problems were helped by restarting memcached.
> After having a closer look at these problems, it appeared that the 
> memory was gradually getting full.
> This was kind of strange, because we use an expiration time of 6 
> hours, which would mean that after a couple of days all items would 
> have to be evicted except those that were put in the last 6 hours.
>
> We suspected that most of the expired items stay in the cache and 
> never get evicted, because the value of the STATS evictions was always 
> 0 and because we found a lot of items older than 6 hours.
>
> The only place I found in the code where evictions are taking place is 
> in do_item_alloc, which means that an item can only be evicted in the 
> case when there is the need for allocating a new item. This means 
> there is no separate garbage collection as such in memcached. This is 
> good, because that would need lots of CPU ticks to run, lowering the 
> performance of the cache.
>
> We found that we need to evict expired items from the cache and 
> therefore we implemented an external garbage collector. We run this 
> program regularly and we found that this solves our problem. This 
> means, memory usage is constantly low now.
>
> And once again:
>
> We would like to make it available as an open source software. Is this 
> interesting to the members of this list?
> Please let me know where we can post it.
>
> Kind regards,
> Ivan
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.danga.com/pipermail/memcached/attachments/20080524/df50c1ca/attachment.html