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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
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