Ivan Krstić wrote:
Gregory Maxwell wrote:
Has memcached's allocator changed? I'm somewhat surprised that that widely varying size of the page text isn't causing us fragmentation problems.
As I mentioned during the hacking days, the allocator granularity and semantics have been improved (along with a pile of other things) by Facebook in what is about to become memcached 1.2.0. If we see fragmentation errors, a switch to 1.2 is in order.
I don't know what you mean by fragmentation. Memcached's problem is fixed distribution of memory between size classes, which can lead to one size class having a very different expiry time to another. I've never heard such a problem referred to as fragmentation. Allocation and deallocation are constant-time operations, so fragmentation of memory within a slab is irrelevant.
I imagine the revision cache would have a similar size distribution to the parser cache, which was the dominant item previously in terms of size.
-- Tim Starling