On 7/22/10 2:02 PM, Jakub Łopuszański wrote:
Well, I beg to differ. We used to have evictions > 0, actually around 200 (per whatever munin counts them), so we used to think, that we have too small number of machines, and kept adding them. After using the patch, the memory usage dropped by 80%, and we have no evictions since a long time, which means, that evictions where misleading, and happened just because LRU sometimes kills fresh items, even though there are lots of outdated keys.
Let me make sure I understand your claim here. You are claiming that the LRU is evicting things even though there are expired items in the slabs? And that expired items are left in the slabs and non-expired items are removed from the slab by the LRU? That is your claim? I just want to be clear.
Moreover it's not like RAM usage "fluctuates wildly". It's kind of constant, or at least periodic, so you can very accurately say if something bad happened, as it would be instantly visible as a deviation from yesterday's charts. Before applying the patch, you could as well not look at the chart at all, as it was more than sure that it always shows 100% usage, which in my opinion gives no clue about what is actually going on. Even if you are afraid of "wildly fluctuating" charts, you will not solve the problem by hiding it, and this is what actually happens if you don't have GC -- the traffic, the number of outdated keys, they all fluctuate, but you just don't see it, if the chart always shows 100% usage...
It has nothing to do with fear. It has to do with managing resources. A sudden peak in evictions is much better than a sudden lack of memory on all my memcached servers. Evictions > OOM.
-- Brian. -------- http://brian.moonspot.net/
