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From dav...@apache.org
Subject [couchdb] 01/03: Remove LRU from ddoc_cache
Date Fri, 16 Jun 2017 21:40:27 GMT
This is an automated email from the ASF dual-hosted git repository.

davisp pushed a commit to branch optimize-ddoc-cache
in repository https://gitbox.apache.org/repos/asf/couchdb.git

commit 834844601b131716beb343fc504e1d166e8348c2
Author: Paul J. Davis <paul.joseph.davis@gmail.com>
AuthorDate: Fri Jun 16 13:29:47 2017 -0500

    Remove LRU from ddoc_cache
    
    This is only a part of the necessary work to optimize the ddoc cache.
    This will not work in production because the ets_lru max_age is not
    implemented so once a ddoc is in the cache it won't be removed unless
    everything stops using it (which for a busy database will be never
    because of the match_newest code).
---
 src/ddoc_cache/src/ddoc_cache.app.src    |   7 +-
 src/ddoc_cache/src/ddoc_cache.erl        |   2 +-
 src/ddoc_cache/src/ddoc_cache.hrl        |  32 +++++
 src/ddoc_cache/src/ddoc_cache_lru.erl    | 221 +++++++++++++++++++++++++++++++
 src/ddoc_cache/src/ddoc_cache_opener.erl | 123 ++++++-----------
 src/ddoc_cache/src/ddoc_cache_sup.erl    |  35 ++---
 src/ddoc_cache/src/ddoc_cache_tables.erl |  64 +++++++++
 7 files changed, 370 insertions(+), 114 deletions(-)

diff --git a/src/ddoc_cache/src/ddoc_cache.app.src b/src/ddoc_cache/src/ddoc_cache.app.src
index a64b2f5..084895e 100644
--- a/src/ddoc_cache/src/ddoc_cache.app.src
+++ b/src/ddoc_cache/src/ddoc_cache.app.src
@@ -21,6 +21,7 @@
         ddoc_cache_util
     ]},
     {registered, [
+        ddoc_cache_tables,
         ddoc_cache_lru,
         ddoc_cache_opener
     ]},
@@ -29,16 +30,10 @@
         stdlib,
         crypto,
         couch_event,
-        ets_lru,
         mem3,
         fabric,
         couch_log,
         couch_stats
     ]},
     {mod, {ddoc_cache_app, []}},
-    {env, [
-        {max_objects, unlimited},
-        {max_size, 104857600}, % 100M
-        {max_lifetime, 60000} % 1m
-    ]}
 ]}.
diff --git a/src/ddoc_cache/src/ddoc_cache.erl b/src/ddoc_cache/src/ddoc_cache.erl
index ed93309..07d89ac 100644
--- a/src/ddoc_cache/src/ddoc_cache.erl
+++ b/src/ddoc_cache/src/ddoc_cache.erl
@@ -91,7 +91,7 @@ open_custom(DbName, Mod) ->
 
 evict(ShardDbName, DDocIds) ->
     DbName = mem3:dbname(ShardDbName),
-    ddoc_cache_opener:evict_docs(DbName, DDocIds).
+    ddoc_cache_lru:evict(DbName, DDocIds).
 
 open(DbName, validation_funs) ->
     open_validation_funs(DbName);
diff --git a/src/ddoc_cache/src/ddoc_cache.hrl b/src/ddoc_cache/src/ddoc_cache.hrl
new file mode 100644
index 0000000..8545914
--- /dev/null
+++ b/src/ddoc_cache/src/ddoc_cache.hrl
@@ -0,0 +1,32 @@
+% 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.
+
+-type dbname() :: iodata().
+-type docid() :: iodata().
+-type doc_hash() :: <<_:128>>.
+-type revision() :: {pos_integer(), doc_hash()}.
+
+-define(CACHE, ddoc_cache_entries).
+-define(ATIMES, ddoc_cache_atimes).
+-define(OPENERS, ddoc_cache_openers).
+
+
+-record(entry, {
+    key,
+    val
+}).
+
+-record(opener, {
+    key,
+    pid,
+    clients
+}).
diff --git a/src/ddoc_cache/src/ddoc_cache_lru.erl b/src/ddoc_cache/src/ddoc_cache_lru.erl
new file mode 100644
index 0000000..9d8c397
--- /dev/null
+++ b/src/ddoc_cache/src/ddoc_cache_lru.erl
@@ -0,0 +1,221 @@
+% 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(ddoc_cache_lru).
+-behaviour(gen_server).
+-vsn(1).
+
+
+-export([
+    start_link/0,
+
+    insert/2,
+    accessed/1,
+    evict/1,
+    evict/2
+]).
+
+-export([
+    init/1,
+    terminate/2,
+    handle_call/3,
+    handle_cast/2,
+    handle_info/2,
+    code_change/3
+]).
+
+-export([
+    handle_db_event/3
+]).
+
+
+-include("ddoc_cache.hrl").
+
+
+-record(st, {
+    keys,
+    time,
+    max_size,
+    evictor
+}).
+
+
+start_link() ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
+
+
+insert(Key, Val) ->
+    gen_server:call(?MODULE, {insert, Key}).
+
+
+accessed(Key) ->
+    gen_server:cast(?MODULE, {accessed, Key}).
+
+
+-spec evict(dbname(), [docid()]) -> ok.
+evict(DbName, DDocIds) ->
+    gen_server:cast(?MODULE, {evict, DbName, DDocIds}).
+
+
+init(_) ->
+    {ok, Keys} = khash:new(),
+    {ok, Evictor} = couch_event:link_listener(
+            ?MODULE, handle_db_event, nil, [all_dbs]
+        ),
+    MaxSize = config:get_integer("ddoc_cache", "max_size", 1000),
+    {ok, #st{
+        keys = Keys,
+        time = 0,
+        max_size = MaxSize,
+        evictor = Evictor
+    }}.
+
+
+terminate(_Reason, St) ->
+    case is_pid(St#st.evictor) of
+        true -> exit(St#st.evictor, kill);
+        false -> ok
+    end,
+    ok.
+
+
+handle_call({insert, Key, Val}, _From, St) ->
+    #st{
+        keys = Keys,
+        time = Time
+    } = St,
+    NewTime = Time + 1,
+    true = ets:insert(?CACHE, #entry{key = Key, val = Val}),
+    true = ets:insert(?ATIMES, {NewTime, Key}),
+    ok = khash:put(Keys, NewTime),
+    {reply, ok, trim(St#st{time = NewTime})};
+
+handle_call(Msg, _From, St) ->
+    {stop, {invalid_call, Msg}, {invalid_call, Msg}, St}.
+
+
+handle_cast({accessed, Key}, _St) ->
+    #st{
+        keys = Keys,
+        time = Time
+    } = St,
+    NewTime = Time + 1,
+    case khash:lookup(Keys, Key) of
+        {value, OldTime} ->
+            true = ets:delete(?ATIMES, OldTime),
+            true = ets:insert(?ATIMES, {NewTime, Key}),
+            ok = khash:put(Keys, NewTime);
+        not_found ->
+            % Likely a client read from the cache while an
+            % eviction message was in our mailbox
+            ok
+    end,
+    {noreply, St};
+
+handle_cast({evict, _} = Msg, St) ->
+    gen_server:abcast(mem3:nodes(), ?MODULE, Msg),
+    {noreply, St};
+
+handle_cast({evict, _, _} = Msg, St) ->
+    gen_server:abcast(mem3:nodes(), ?MODULE, Msg),
+    {noreply, St};
+
+handle_cast({do_evict, DbName} = Msg, St) ->
+    Pattern = #entry{
+        key = {DbName, '$1', '_'},
+        val = '_',
+        _ = '_'
+    },
+    DDocIds = lists:flatten(ets:match(?CACHE, Pattern)),
+    handle_cast({do_evict, DbName, DDocIds});
+
+handle_cast({do_evict, DbName, DDocIds}, St) ->
+    Pattern = #entry{
+        key = {DbName, '$1'},
+        val = '_',
+        _ = '_'
+    },
+    CustomKeys = lists:flatten(ets:match(?CACHE, Pattern)),
+    lists:foreach(fun(Mod) ->
+        ets:delete(?CACHE, {DbName, Mod})
+    end, CustomKeys),
+    lists:foreach(fun(DDocId) ->
+        RevPattern = #entry{
+            key = {DbName, DDocId, '$1'},
+            val = '_',
+            _ = '_'
+        },
+        Revs = lists:flatten(ets:match(?CACHE, RevPattern)),
+        lists:foreach(fun(Rev) ->
+            ets:delete(?CACHE, {DbName, DDocId, Rev})
+        end, Revs)
+    end, DDocIds),
+    {noreply, St};
+
+handle_cast(Msg, St) ->
+    {stop, {invalid_cast, Msg}, St}.
+
+
+handle_info({'EXIT', Pid, Reason}, #st{evictor=Pid}=St) ->
+    couch_log:error("ddoc_cache_opener evictor died ~w", [Reason]),
+    {ok, Evictor} = couch_event:link_listener(
+            ?MODULE, handle_db_event, nil, [all_dbs]
+        ),
+    {noreply, St#st{evictor=Evictor}};
+
+handle_info(Msg, St) ->
+    {stop, {invalid_info, Msg}, St}.
+
+
+code_change(_OldVsn, St, _Extra) ->
+    {ok, St}.
+
+
+handle_db_event(ShardDbName, created, St) ->
+    gen_server:cast(?MODULE, {evict, mem3:dbname(ShardDbName)}),
+    {ok, St};
+
+handle_db_event(ShardDbName, deleted, St) ->
+    gen_server:cast(?MODULE, {evict, mem3:dbname(ShardDbName)}),
+    {ok, St};
+
+handle_db_event(_DbName, _Event, St) ->
+    {ok, St}.
+
+
+trim(St) ->
+    #st{
+        keys = Keys,
+        max_size = MaxSize
+    } = St,
+    case khash:size(Keys) > MaxSize of
+        true ->
+            case ets:first(?ATIMES) of
+                '$end_of_table' ->
+                    St;
+                ATime ->
+                    trim(remove(St, ATime))
+            end;
+        false ->
+            St
+    end.
+
+
+remove(St, ATime) ->
+    #st{
+        keys = Keys
+    } = St,
+    {value, Key} = khash:lookup(Keys, ATime),
+    true = ets:delete(?CACHE, Key),
+    true = ets:delete(?ATIMES, ATime),
+    ok = khash:del(Keys, Key),
+    St.
diff --git a/src/ddoc_cache/src/ddoc_cache_opener.erl b/src/ddoc_cache/src/ddoc_cache_opener.erl
index b76a228..a4adffc 100644
--- a/src/ddoc_cache/src/ddoc_cache_opener.erl
+++ b/src/ddoc_cache/src/ddoc_cache_opener.erl
@@ -35,7 +35,6 @@
     open_doc/2,
     open_doc/3,
     open_validation_funs/1,
-    evict_docs/2,
     lookup/1,
     match_newest/1,
     recover_doc/2,
@@ -43,29 +42,17 @@
     recover_validation_funs/1
 ]).
 -export([
-    handle_db_event/3
-]).
--export([
     fetch_doc_data/1
 ]).
 
--define(CACHE, ddoc_cache_lru).
--define(OPENING, ddoc_cache_opening).
+-include("ddoc_cache.hrl").
 
--type dbname() :: iodata().
--type docid() :: iodata().
--type doc_hash() :: <<_:128>>.
--type revision() :: {pos_integer(), doc_hash()}.
 
--record(opener, {
-    key,
-    pid,
-    clients
-}).
+-define(LRU, ddoc_cache_lru).
+
 
 -record(st, {
-    db_ddocs,
-    evictor
+    db_ddocs
 }).
 
 start_link() ->
@@ -86,14 +73,12 @@ open_validation_funs(DbName) ->
     Resp = gen_server:call(?MODULE, {open, {DbName, validation_funs}}, infinity),
     handle_open_response(Resp).
 
--spec evict_docs(dbname(), [docid()]) -> ok.
-evict_docs(DbName, DocIds) ->
-    gen_server:cast(?MODULE, {evict, DbName, DocIds}).
 
 lookup(Key) ->
-    try ets_lru:lookup_d(?CACHE, Key) of
-        {ok, _} = Resp ->
-            Resp;
+    try ets:lookup(?CACHE, Key) of
+        [#entry{key = Key, val = Val}] ->
+            ddoc_cache_lru:accessed(Key),
+            {ok, Val};
         _ ->
             missing
     catch
@@ -102,10 +87,19 @@ lookup(Key) ->
     end.
 
 match_newest(Key) ->
-    try ets_lru:match_object(?CACHE, Key, '_') of
+    Pattern = #entry{
+        key = Key,
+        val = '_',
+        _ = '_'
+    },
+    try ets:match_object(?CACHE, Pattern) of
         [] ->
             missing;
-        Docs ->
+        Entries ->
+            Docs = lists:map(fun(#entry{key = K, val = V}) ->
+                ddoc_cache_lru:accessed(K),
+                V
+            end, Entries),
             Sorted = lists:sort(
                 fun (#doc{deleted=DelL, revs=L}, #doc{deleted=DelR, revs=R}) ->
                     {not DelL, L} > {not DelR, R}
@@ -133,40 +127,22 @@ recover_validation_funs(DbName) ->
     end, DDocs),
     {ok, Funs}.
 
-handle_db_event(ShardDbName, created, St) ->
-    gen_server:cast(?MODULE, {evict, mem3:dbname(ShardDbName)}),
-    {ok, St};
-handle_db_event(ShardDbName, deleted, St) ->
-    gen_server:cast(?MODULE, {evict, mem3:dbname(ShardDbName)}),
-    {ok, St};
-handle_db_event(_DbName, _Event, St) ->
-    {ok, St}.
 
 init(_) ->
     process_flag(trap_exit, true),
-    _ = ets:new(?OPENING, [set, protected, named_table, {keypos, #opener.key}]),
-    {ok, Evictor} = couch_event:link_listener(
-            ?MODULE, handle_db_event, nil, [all_dbs]
-        ),
-    {ok, #st{
-        evictor = Evictor
-    }}.
-
-terminate(_Reason, St) ->
-    case is_pid(St#st.evictor) of
-        true -> exit(St#st.evictor, kill);
-        false -> ok
-    end,
+    {ok, #st{}}.
+
+terminate(_Reason, _St) ->
     ok.
 
 handle_call({open, OpenerKey}, From, St) ->
-    case ets:lookup(?OPENING, OpenerKey) of
+    case ets:lookup(?OPENERS, OpenerKey) of
         [#opener{clients=Clients}=O] ->
-            ets:insert(?OPENING, O#opener{clients=[From | Clients]}),
+            ets:insert(?OPENERS, O#opener{clients=[From | Clients]}),
             {noreply, St};
         [] ->
             Pid = spawn_link(?MODULE, fetch_doc_data, [OpenerKey]),
-            ets:insert(?OPENING, #opener{key=OpenerKey, pid=Pid, clients=[From]}),
+            ets:insert(?OPENERS, #opener{key=OpenerKey, pid=Pid, clients=[From]}),
             {noreply, St}
     end;
 
@@ -174,38 +150,19 @@ handle_call(Msg, _From, St) ->
     {stop, {invalid_call, Msg}, {invalid_call, Msg}, St}.
 
 
-handle_cast({evict, DbName}, St) ->
-    gen_server:abcast(mem3:nodes(), ?MODULE, {do_evict, DbName}),
-    {noreply, St};
-
-handle_cast({evict, DbName, DDocIds}, St) ->
-    gen_server:abcast(mem3:nodes(), ?MODULE, {do_evict, DbName, DDocIds}),
+% The do_evict clauses are upgrades while we're
+% in a rolling reboot.
+handle_cast({do_evict, _} = Msg, St) ->
+    gen_server:cast(?LRU, Msg),
     {noreply, St};
 
-handle_cast({do_evict, DbName}, St) ->
-    DDocIds = lists:flatten(ets_lru:match(?CACHE, {DbName, '$1', '_'}, '_')),
-    handle_cast({do_evict, DbName, DDocIds}, St);
-
-handle_cast({do_evict, DbName, DDocIds}, St) ->
-    CustomKeys = lists:flatten(ets_lru:match(?CACHE, {DbName, '$1'}, '_')),
-    lists:foreach(fun(Mod) ->
-        ets_lru:remove(?CACHE, {DbName, Mod})
-    end, CustomKeys),
-    lists:foreach(fun(DDocId) ->
-        Revs = ets_lru:match(?CACHE, {DbName, DDocId, '$1'}, '_'),
-        lists:foreach(fun([Rev]) ->
-            ets_lru:remove(?CACHE, {DbName, DDocId, Rev})
-        end, Revs)
-    end, DDocIds),
+handle_cast({do_evict, _, _}, St) ->
+    gen_server:cast(?LRU, Msg)
     {noreply, St};
 
 handle_cast(Msg, St) ->
     {stop, {invalid_cast, Msg}, St}.
 
-handle_info({'EXIT', Pid, Reason}, #st{evictor=Pid}=St) ->
-    couch_log:error("ddoc_cache_opener evictor died ~w", [Reason]),
-    {ok, Evictor} = couch_event:link_listener(?MODULE, handle_db_event, nil, [all_dbs]),
-    {noreply, St#st{evictor=Evictor}};
 
 handle_info({'EXIT', _Pid, {open_ok, OpenerKey, Resp}}, St) ->
     respond(OpenerKey, {open_ok, Resp}),
@@ -217,10 +174,10 @@ handle_info({'EXIT', _Pid, {open_error, OpenerKey, Type, Error}}, St)
->
 
 handle_info({'EXIT', Pid, Reason}, St) ->
     Pattern = #opener{pid=Pid, _='_'},
-    case ets:match_object(?OPENING, Pattern) of
+    case ets:match_object(?OPENERS, Pattern) of
         [#opener{key=OpenerKey, clients=Clients}] ->
-            _ = [gen_server:reply(C, {error, Reason}) || C <- Clients],
-            ets:delete(?OPENING, OpenerKey),
+            [gen_server:reply(C, {error, Reason}) || C <- Clients],
+            ets:delete(?OPENERS, OpenerKey),
             {noreply, St};
         [] ->
             {stop, {unknown_pid_died, {Pid, Reason}}, St}
@@ -238,14 +195,14 @@ code_change(_OldVsn, State, _Extra) ->
                     ({dbname(), docid(), revision()}) -> no_return().
 fetch_doc_data({DbName, validation_funs}=OpenerKey) ->
     {ok, Funs} = recover_validation_funs(DbName),
-    ok = ets_lru:insert(?CACHE, OpenerKey, Funs),
+    ok = ddoc_cache_lru:insert(OpenerKey, Funs),
     exit({open_ok, OpenerKey, {ok, Funs}});
 fetch_doc_data({DbName, Mod}=OpenerKey) when is_atom(Mod) ->
     % This is not actually a docid but rather a custom cache key.
     % Treat the argument as a code module and invoke its recover function.
     try Mod:recover(DbName) of
         {ok, Result} ->
-            ok = ets_lru:insert(?CACHE, OpenerKey, Result),
+            ok = ddoc_cache_lru:insert(OpenerKey, Result),
             exit({open_ok, OpenerKey, {ok, Result}});
         Else ->
             exit({open_ok, OpenerKey, Else})
@@ -258,7 +215,7 @@ fetch_doc_data({DbName, DocId}=OpenerKey) ->
         {ok, Doc} ->
             {RevDepth, [RevHash| _]} = Doc#doc.revs,
             Rev = {RevDepth, RevHash},
-            ok = ets_lru:insert(?CACHE, {DbName, DocId, Rev}, Doc),
+            ok = ddoc_cache_lru:insert({DbName, DocId, Rev}, Doc),
             exit({open_ok, OpenerKey, {ok, Doc}});
         Else ->
             exit({open_ok, OpenerKey, Else})
@@ -269,7 +226,7 @@ fetch_doc_data({DbName, DocId}=OpenerKey) ->
 fetch_doc_data({DbName, DocId, Rev}=OpenerKey) ->
     try recover_doc(DbName, DocId, Rev) of
         {ok, Doc} ->
-            ok = ets_lru:insert(?CACHE, {DbName, DocId, Rev}, Doc),
+            ok = ddoc_cache_lru:insert({DbName, DocId, Rev}, Doc),
             exit({open_ok, OpenerKey, {ok, Doc}});
         Else ->
             exit({open_ok, OpenerKey, Else})
@@ -287,6 +244,6 @@ handle_open_response(Resp) ->
     end.
 
 respond(OpenerKey, Resp) ->
-    [#opener{clients=Clients}] = ets:lookup(?OPENING, OpenerKey),
+    [#opener{clients=Clients}] = ets:lookup(?OPENERS, OpenerKey),
     _ = [gen_server:reply(C, Resp) || C <- Clients],
-    ets:delete(?OPENING, OpenerKey).
+    ets:delete(?OPENERS, OpenerKey).
diff --git a/src/ddoc_cache/src/ddoc_cache_sup.erl b/src/ddoc_cache/src/ddoc_cache_sup.erl
index 85e90b3..ddb1232 100644
--- a/src/ddoc_cache/src/ddoc_cache_sup.erl
+++ b/src/ddoc_cache/src/ddoc_cache_sup.erl
@@ -27,12 +27,20 @@ start_link() ->
 init([]) ->
     Children = [
         {
+            ddoc_cache_tables,
+            {ddoc_cache_tables, start_link, []},
+            permanent,
+            5000,
+            worker,
+            [ddoc_cache_tables]
+        },
+        {
             ddoc_cache_lru,
-            {ets_lru, start_link, [ddoc_cache_lru, lru_opts()]},
+            {ddoc_cache_lru, start_link, []},
             permanent,
             5000,
             worker,
-            [ets_lru]
+            [ddoc_cache_lru]
         },
         {
             ddoc_cache_opener,
@@ -43,25 +51,4 @@ init([]) ->
             [ddoc_cache_opener]
         }
     ],
-    {ok, {{one_for_one, 5, 10}, Children}}.
-
-
-lru_opts() ->
-    case application:get_env(ddoc_cache, max_objects) of
-        {ok, MxObjs} when is_integer(MxObjs), MxObjs >= 0 ->
-            [{max_objects, MxObjs}];
-        _ ->
-            []
-    end ++
-    case application:get_env(ddoc_cache, max_size) of
-        {ok, MxSize} when is_integer(MxSize), MxSize >= 0 ->
-            [{max_size, MxSize}];
-        _ ->
-            []
-    end ++
-    case application:get_env(ddoc_cache, max_lifetime) of
-        {ok, MxLT} when is_integer(MxLT), MxLT >= 0 ->
-            [{max_lifetime, MxLT}];
-        _ ->
-            []
-    end.
+    {ok, {{one_for_all, 5, 10}, Children}}.
diff --git a/src/ddoc_cache/src/ddoc_cache_tables.erl b/src/ddoc_cache/src/ddoc_cache_tables.erl
new file mode 100644
index 0000000..9b35943
--- /dev/null
+++ b/src/ddoc_cache/src/ddoc_cache_tables.erl
@@ -0,0 +1,64 @@
+% 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(ddoc_cache_tables).
+-behaviour(gen_server).
+-vsn(1).
+
+
+-export([
+    start_link/0
+]).
+
+-export([
+    init/1,
+    terminate/2,
+    handle_call/3,
+    handle_cast/2,
+    handle_info/2,
+    code_change/3
+]).
+
+
+-include("ddoc_cache.hrl").
+
+
+start_link() ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
+
+
+init(_) ->
+    BaseOpts = [public, named_table],
+    ets:new(?CACHE, [set, {read_concurrency, true}] ++ BaseOpts),
+    ets:new(?ATIMES, [sorted_set] ++ BaseOpts),
+    ets:new(?OPENING, [set, {keypos, #opener.key}] ++ BaseOpts),
+    {ok, nil}.
+
+
+terminate(_Reason, _St) ->
+    ok.
+
+
+handle_call(Msg, _From, St) ->
+    {stop, {invalid_call, Msg}, {invalid_call, Msg}, St}.
+
+
+handle_cast(Msg, St) ->
+    {stop, {invalid_cast, Msg}, St}.
+
+
+handle_info(Msg, St) ->
+    {stop, {invalid_info, Msg}, St}.
+
+
+code_change(_OldVsn, St, _Extra) ->
+    {ok, St}.

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