high-performance (k,v) mem storage, designed to use as cache.
every (k,v) is called an item in mc.
main data struture:
item: (k,v) in memcached slabs: slabs sub system hash: item index lru: lru queue
| item ITEM_SLABBED : item not used but alloced in slabs, aka free in slabs ITEM_CHUNK : item chunk data ITEM_CHUNKED : item chunk head ITEM_FETCHED : item accessed at least once after set, i.e. item active ITEM_LINKED : item linked into lru queue and hash item state trans: ITEM_SLABBED -> ITEM_CHUNK -> ITEM_CHUNKED -> ITEM_FETCHED -> ITEM_LINKED -> |
|---|
| slabs |
| slabs module: slabsclass[64]: slots[]: slab_list[]: |
| rebalance |
thread wait for rebalance signal on init, wait for slab_reassaign ; |
client command slabs reassign <src> <dst> or eviction when automove=2 or lru_maintain when automove=1; |
| start reassign process if slabs > 2; |
hash
init rehash
lru