rewrite mem3_cache to use continuous _changes feed

1 files changed, 71 insertions, 61 deletions

diff --git a/src/mem3_cache.erl b/src/mem3_cache.erl
index 8f5c372a..532a023a 100644
--- a/src/mem3_cache.erl
+++ b/src/mem3_cache.erl
@@ -5,87 +5,97 @@
 
 -export([start_link/0]).
 
+-record(state, {changes_pid}).
+
 -include("mem3.hrl").
 
 start_link() ->
     gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
 
 init([]) ->
-    ets:new(partitions, [bag, protected, named_table, {keypos,#shard.dbname}]),
-    ets:new(memnodes, [bag, protected, named_table]),
-    cache_dbs(),
-    Self = self(),
-    couch_db_update_notifier:start_link(fun({updated, <<"dbs">>}) ->
-        Self ! rebuild_dbs_cache;
-    (_) -> ok end),
-    {ok, nil}.
+    ets:new(partitions, [bag, public, named_table, {keypos,#shard.dbname}]),
+    {Pid, _} = spawn_monitor(fun() -> listen_for_changes(0) end),
+    {ok, #state{changes_pid = Pid}}.
 
-handle_call(_Msg, _From, State) ->
-    {reply, ok, State}.
+handle_call(_Call, _From, State) ->
+    {noreply, State}.
 
 handle_cast(_Msg, State) ->
     {noreply, State}.
 
-handle_info(rebuild_dbs_cache, State) ->
-    receive rebuild_dbs_cache ->
-        handle_info(rebuild_dbs_cache, State)
-    after 0 -> ok end,
-    T0 = now(),
-    ?LOG_INFO("rebuilding dbs DB cache", []),
-    ets:delete_all_objects(partitions),
-    ets:delete_all_objects(memnodes),
-    cache_dbs(),
-    ?LOG_INFO("rebuild of dbs DB cache complete in ~p ms",
-        [round(timer:now_diff(now(),T0)/1000)]),
+handle_info({'DOWN', _, _, Pid, Reason}, #state{changes_pid=Pid} = State) ->
+    ?LOG_INFO("~p changes listener died ~p", [?MODULE, Reason]),
+    Seq = case Reason of {seq, EndSeq} -> EndSeq; _ -> 0 end,
+    timer:send_after(5000, {start_listener, Seq}),
+    {noreply, State};
+handle_info({start_listener, Seq}, State) ->
+    {NewPid, _} = spawn_monitor(fun() -> listen_for_changes(Seq) end),
+    {noreply, State#state{changes_pid=NewPid}};
+handle_info(_Msg, State) ->
     {noreply, State}.
 
-terminate(_Reason, _State) ->
+terminate(_Reason, #state{changes_pid=Pid}) ->
+    exit(Pid, kill),
     ok.
 
 code_change(_OldVsn, State, _Extra) ->
     {ok, State}.
 
-cache_dbs() ->
-    try couch_db:open(<<"dbs">>, []) of
+%% internal functions
+
+listen_for_changes(Since) ->
+    DbName = ?l2b(couch_config:get("mem3", "db", "dbs")),
+    {ok, Db} = ensure_exists(DbName),
+    Args = #changes_args{
+        feed = "continuous",
+        since = Since,
+        heartbeat = true,
+        include_docs = true
+    },
+    ChangesFun = couch_changes:handle_changes(Args, nil, Db),
+    ChangesFun(fun changes_callback/2).
+
+ensure_exists(DbName) ->
+    Options = [{user_ctx, #user_ctx{roles=[<<"_admin">>]}}],
+    case couch_db:open(DbName, Options) of
     {ok, Db} ->
-        Bt = Db#db.id_tree,
-        FoldFun = fun(#full_doc_info{id=Id, deleted=false} = FullDocInfo, _, _) ->
-            {ok, Doc} = couch_db:open_doc_int(Db, FullDocInfo, []),
-            {Props} = couch_doc:to_json_obj(Doc, []),
-            cache_map(Id, Props),
-            cache_nodes(Id, Props),
-            {ok, true};
-        (_, _, _) ->
-            {ok, nil}
-        end,
-        couch_btree:foldl(Bt, FoldFun, nil),
-        couch_db:close(Db)
-    catch exit:{noproc,{gen_server,call,[couch_server|_]}} ->
-        timer:sleep(1000),
-        exit(couch_server_is_dead)
+        {ok, Db};
+    _ -> 
+        couch_server:create(DbName, Options)
     end.
 
-cache_map(Id, Props) ->
-    Map = couch_util:get_value(<<"map">>, Props, []),
-    lists:foreach(fun({[{<<"node">>,Node},{<<"b">>,Beg},{<<"e">>,End}]}) ->
-        Part = #shard{
-            name = partitions:shard_name(Beg, Id),
-            dbname = Id,
-            node = to_atom(Node),
-            range = [Beg,End]
-        },
-        ets:insert(partitions, Part)
-    end, Map).
-
-cache_nodes(Id, Props) ->
-    Nodes = couch_util:get_value(<<"nodes">>, Props, []),
-    lists:foreach(fun({[{<<"order">>,Order},{<<"node">>, Node},{<<"options">>,Opts}]}) ->
-        ets:insert(memnodes, {Id, {Order, to_atom(Node), Opts}})
-    end, Nodes).
+changes_callback(start, _) ->
+    {ok, nil};
+changes_callback({stop, EndSeq}, _) ->
+    exit({seq, EndSeq});
+changes_callback({change, {Change}, _}, _) ->
+    DbName = couch_util:get_value(id, Change),
+    case couch_util:get_value(deleted, Change, false) of
+    true ->
+        ets:delete(partitions, DbName);
+    false ->
+        case couch_util:get_value(doc, Change) of
+        {error, Reason} ->
+            ?LOG_ERROR("missing partition table for ~s: ~p", [DbName, Reason]);
+        {Doc} ->
+            ets:delete(partitions, DbName),
+            cache_partition_table(DbName, Doc)
+        end
+    end,
+    {ok, couch_util:get_value(seq, Change)};
+changes_callback(timeout, _) ->
+    {ok, nil}.
+
+cache_partition_table(DbName, Doc) ->
+    ets:insert(partitions, lists:map(fun({Map}) ->
+        Begin = couch_util:get_value(<<"b">>, Map),
+        #shard{
+            name = mem3_util:shard_name(Begin, DbName),
+            dbname = DbName,
+            node = to_atom(couch_util:get_value(<<"node">>, Map)),
+            range = [Begin, couch_util:get_value(<<"e">>, Map)]
+        }
+    end, couch_util:get_value(<<"map">>, Doc, {[]}))).
 
 to_atom(Node) when is_binary(Node) ->
-    list_to_atom(binary_to_list(Node));
-to_atom(Node) when is_atom(Node) ->
-    Node.
-
-%{ok, ets:insert(dbs_cache, {Id, Props})};
+    list_to_atom(binary_to_list(Node)).