Revert couch_lru to use gb_trees

Recently couch_lru was changed to use ets tables.

During eprof profiling it showed improved performance however recently in a
larger test with more concurrent updates and 5000 max dbs open it showed a
significant degradation compared to the previous (gb_tree-based) version.

GH Issue #528

2 files changed, 27 insertions, 144 deletions

diff --git a/src/couch/src/couch_lru.erl b/src/couch/src/couch_lru.erl
index b79286ee0..b58a623d6 100644
--- a/src/couch/src/couch_lru.erl
+++ b/src/couch/src/couch_lru.erl
@@ -16,39 +16,33 @@
 -include_lib("couch/include/couch_db.hrl").
 
 new() ->
-    Updates = ets:new(couch_lru_updates, [ordered_set]),
-    Dbs = ets:new(couch_lru_dbs, [set]),
-    {0, Updates, Dbs}.
-
-insert(DbName, {Count, Updates, Dbs}) ->
-    update(DbName, {Count, Updates, Dbs}).
-
-update(DbName, {Count, Updates, Dbs}) ->
-    case ets:lookup(Dbs, DbName) of
-        [] ->
-            true = ets:insert(Dbs, {DbName, Count});
-        [{DbName, OldCount}] ->
-            true = ets:update_element(Dbs, DbName, {2, Count}),
-            true = ets:delete(Updates, {OldCount, DbName})
-    end,
-    true = ets:insert(Updates, {{Count, DbName}}),
-    {Count + 1, Updates, Dbs}.
-
-
-close({Count, Updates, Dbs}) ->
-    case close_int(ets:next(Updates, {-1, <<>>}), Updates, Dbs) of
-        true ->
-            {true, {Count, Updates, Dbs}};
-        false ->
-            false
+    {gb_trees:empty(), dict:new()}.
+
+insert(DbName, {Tree0, Dict0}) ->
+    Lru = erlang:now(),
+    {gb_trees:insert(Lru, DbName, Tree0), dict:store(DbName, Lru, Dict0)}.
+
+update(DbName, {Tree0, Dict0}) ->
+    case dict:find(DbName, Dict0) of
+    {ok, Old} ->
+        New = erlang:now(),
+        Tree = gb_trees:insert(New, DbName, gb_trees:delete(Old, Tree0)),
+        Dict = dict:store(DbName, New, Dict0),
+        {Tree, Dict};
+    error ->
+        % We closed this database before processing the update.  Ignore
+        {Tree0, Dict0}
     end.
 
+%% Attempt to close the oldest idle database.
+close({Tree, _} = Cache) ->
+    close_int(gb_trees:next(gb_trees:iterator(Tree)), Cache).
 
 %% internals
 
-close_int('$end_of_table', _Updates, _Dbs) ->
+close_int(none, _) ->
     false;
-close_int({_Count, DbName} = Key, Updates, Dbs) ->
+close_int({Lru, DbName, Iter}, {Tree, Dict} = Cache) ->
     case ets:update_element(couch_dbs, DbName, {#db.fd_monitor, locked}) of
     true ->
         [#db{main_pid = Pid} = Db] = ets:lookup(couch_dbs, DbName),
@@ -56,16 +50,14 @@ close_int({_Count, DbName} = Key, Updates, Dbs) ->
             true = ets:delete(couch_dbs, DbName),
             true = ets:delete(couch_dbs_pid_to_name, Pid),
             exit(Pid, kill),
-            true = ets:delete(Updates, Key),
-            true = ets:delete(Dbs, DbName),
-            true;
+            {true, {gb_trees:delete(Lru, Tree), dict:erase(DbName, Dict)}};
         false ->
             true = ets:update_element(couch_dbs, DbName, {#db.fd_monitor, nil}),
             couch_stats:increment_counter([couchdb, couch_server, lru_skip]),
-            close_int(ets:next(Updates, Key), Updates, Dbs)
+            close_int(gb_trees:next(Iter), update(DbName, Cache))
         end;
     false ->
-        true = ets:delete(Updates, Key),
-        true = ets:delete(Dbs, DbName),
-        close_int(ets:next(Updates, Key), Updates, Dbs)
-    end.
+        NewTree = gb_trees:delete(Lru, Tree),
+        NewIter = gb_trees:iterator(NewTree),
+        close_int(gb_trees:next(NewIter), {NewTree, dict:erase(DbName, Dict)})
+end.
diff --git a/src/couch/test/couch_lru_tests.erl b/src/couch/test/couch_lru_tests.erl
deleted file mode 100644
index 15598358f..000000000
--- a/src/couch/test/couch_lru_tests.erl
+++ /dev/null
@@ -1,109 +0,0 @@
-% Licensed under the Apache License, Version 2.0 (the "License"); you may not
-% use this file except in compliance with the License. You may obtain a copy of
-% the License at
-%
-%   http://www.apache.org/licenses/LICENSE-2.0
-%
-% Unless required by applicable law or agreed to in writing, software
-% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-% License for the specific language governing permissions and limitations under
-% the License.
-
--module(couch_lru_tests).
-
--include_lib("couch/include/couch_eunit.hrl").
--include_lib("couch/include/couch_db.hrl").
-
-
-setup() ->
-    ok = meck:new(couch_db, [passthrough]),
-    ets:new(couch_dbs, [set, public, named_table, {keypos, #db.name}]),
-    ets:new(couch_dbs_pid_to_name, [set, public, named_table]),
-    couch_lru:new().
-
-teardown(_) ->
-    ets:delete(couch_dbs),
-    ets:delete(couch_dbs_pid_to_name),
-    (catch meck:unload(couch_db)).
-
-new_test_() ->
-    {setup,
-        fun() -> couch_lru:new() end,
-        fun(Lru) ->
-            ?_assertMatch({0, _, _}, Lru)
-        end
-    }.
-
-insert_test_() ->
-    {setup,
-        fun() -> couch_lru:new() end,
-        fun(Lru) ->
-            Key = <<"test">>,
-            {1, Updates, Dbs} = couch_lru:insert(Key, Lru),
-            [
-                ?_assertEqual(1, ets_size(Dbs)),
-                ?_assert(ets:member(Dbs, Key)),
-                ?_assertEqual(1, ets_size(Updates)),
-                ?_assert(ets:member(Updates, {0, Key}))
-            ]
-        end
-    }.
-
-insert_same_test_() ->
-    {setup,
-        fun() -> couch_lru:new() end,
-        fun(Lru) ->
-            Key = <<"test">>,
-            Lru1 = {1, Updates, Dbs} = couch_lru:insert(Key, Lru),
-            {2, Updates, Dbs} = couch_lru:insert(Key, Lru1),
-            [
-                ?_assertEqual(1, ets_size(Dbs)),
-                ?_assert(ets:member(Dbs, Key)),
-                ?_assertEqual(1, ets_size(Updates)),
-                ?_assert(ets:member(Updates, {1, Key}))
-            ]
-        end
-    }.
-
-update_test_() ->
-    {setup,
-        fun() -> couch_lru:new() end,
-        fun(Lru) ->
-            Key = <<"test">>,
-            Lru1 = {1, Updates, Dbs} = couch_lru:update(Key, Lru),
-            {2, Updates, Dbs} = couch_lru:update(Key, Lru1),
-            [
-                ?_assertEqual(1, ets_size(Dbs)),
-                ?_assert(ets:member(Dbs, Key)),
-                ?_assertEqual(1, ets_size(Updates)),
-                ?_assert(ets:member(Updates, {1, Key}))
-            ]
-        end
-    }.
-
-close_test_() ->
-    {setup,
-        fun setup/0,
-        fun teardown/1,
-        fun(Lru) ->
-            ok = meck:expect(couch_db, is_idle, 1, true),
-            {ok, Lru1} = add_record(Lru, <<"test1">>, c:pid(0, 1001, 0)),
-            {ok, Lru2} = add_record(Lru1, <<"test2">>, c:pid(0, 2001, 0)),
-            {true, {2, Updates, Dbs}} = couch_lru:close(Lru2),
-            [
-                ?_assertEqual(1, ets_size(Dbs)),
-                ?_assert(ets:member(Dbs, <<"test2">>)),
-                ?_assertEqual(1, ets_size(Updates)),
-                ?_assert(ets:member(Updates, {1, <<"test2">>}))
-            ]
-        end
-    }.
-
-add_record(Lru, Key, Pid) ->
-    true = ets:insert(couch_dbs, #db{name = Key, main_pid = Pid}),
-    true = ets:insert(couch_dbs_pid_to_name, {Pid, Key}),
-    {ok, couch_lru:insert(Key, Lru)}.
-
-ets_size(Ets) ->
-    proplists:get_value(size, ets:info(Ets)).