Eviction, Ejection, working set management

Need more content here:

http://www.couchbase.com/docs/couchbase-manual-2.0/couchbase-introduction-architecture-eviction.html

-Describe new logic for eviction as of 2.0
-Tie into Access Logs topic
-Any command line which impacts this behavior

Input from Liang:

-ejection vs eviction: eviction a concept from memcached, it means the entire items (key, metadata and value) removed from RAM. Ejection is what we do now for 1.8 and 2.0: the value is removed but the keys and metadata still in memory
-warmup process - two iterations occur: firs tkeys and metadata loaded, then values for keys in access log. See info added on disk warmup on access scanner.
-expiry pager: remove expired items from memory. A disk cleanup process
-item pager: eject items if high water mark reached, eject hose that are not dirty or need to be replicated to node in cluster. High water mark configurable

-item pager: looks at NRU or if high water still breached, eject random, use % active vs replica. Also configurable via cbepctl
-goal improve memory efficiency, maintain balance of active/replica data.

defaults ejection % 40% for active with 50% cap, One parameter - adjust two items: active/replica-as-remainder

goal reach low water mark, but if under HWM, timer pager stops. if not repeats until under.
-NRU - replicated. if mutation on item, set to true. this true value replicated to other node in cluster. 1 bit.
-access scanner - adds all NRU true to access log, then sets all items to false after pass, thereby influencing item pager
-(percentage memory to be free) = (total memory - lwm)/ total memory

-config hwm at each node? Must be reset after node failure. Config are in memory on node.
-high active ratio reduce cache miss,
-too low replica% - if replica node promoted, will experience cache misses - post rebalance, post rebalance

Input from Jin on Configurations:

-Hi, you can change the default water marks by "flush_param [mem_high_wat/mem_low_wat] value" via cbepctl.

You can change the default percentage of active vbuckets being ejected items by item pager by
"flush_param pager_active_vb_pcnt value" where value is btwn 0 and 50%.