Add an index keyed on LRU for faster candidate ID

Our current implementation for closing an LRU DB involves a full scan
of a public ets table.  This scan blocks all other activity in
couch_server and can become a serious bottleneck when the LRU cache hit
rate drops too low.  In the worst-case all_dbs_active scenario we end up
with O(N**2) algorithmic complexity.

This patch adds a new index keyed on LRU for faster access to the least
recently used databases.  It also moves the ets table to a dict on the
couch_server heap.  The downside is an increased message rate inbound on
the couch_server, as clients are no longer allowed to update the LRU
data structures without sending a message.

BugzID: 12879

Conflicts:
	apps/couch/src/couch_server.erl

0 files changed, 0 insertions, 0 deletions