diff --git a/src/ejabberd_redis.erl b/src/ejabberd_redis.erl
index 8eeb19607..740b552f4 100644
--- a/src/ejabberd_redis.erl
+++ b/src/ejabberd_redis.erl
@@ -55,7 +55,11 @@
 		num :: pos_integer(),
 		pending_q :: p1_queue:queue()}).
 
--type redis_error() :: {error, binary() | atom()}.
+-type redis_error() :: {error, binary() | timeout | disconnected}.
+-type redis_reply() :: binary() | [binary()].
+-type redis_command() :: [binary()].
+-type redis_pipeline() :: [redis_command()].
+-type state() :: #state{}.
 
 %%%===================================================================
 %%% API
@@ -73,13 +77,15 @@ get_connection(I) ->
       iolist_to_binary(
 	[atom_to_list(?MODULE), "_connection_", integer_to_list(I)])).
 
+-spec q(redis_command()) -> {ok, redis_reply()} | redis_error().
 q(Command) ->
     call(get_worker(), {q, Command}, ?MAX_RETRIES).
 
+-spec qp(redis_pipeline()) -> {ok, [redis_reply()]} | redis_error().
 qp(Pipeline) ->
     call(get_worker(), {qp, Pipeline}, ?MAX_RETRIES).
 
--spec multi(fun(() -> any())) -> {ok, list()} | redis_error().
+-spec multi(fun(() -> any())) -> {ok, [redis_reply()]} | redis_error().
 multi(F) ->
     case erlang:get(?TR_STACK) of
 	undefined ->
@@ -98,7 +104,7 @@ multi(F) ->
 		    erlang:raise(E, R, erlang:get_stacktrace())
 	    end;
 	_ ->
-	    {error, nested_transaction}
+	    erlang:error(nested_transaction)
     end.
 
 -spec get(iodata()) -> {ok, undefined | binary()} | redis_error().
@@ -107,7 +113,7 @@ get(Key) ->
 	undefined ->
 	    q([<<"GET">>, Key]);
 	_ ->
-	    {error, transaction_unsupported}
+	    erlang:error(transaction_unsupported)
     end.
 
 -spec set(iodata(), iodata()) -> ok | redis_error() | queued.
@@ -174,7 +180,7 @@ smembers(Set) ->
 	undefined ->
 	    q([<<"SMEMBERS">>, Set]);
 	_ ->
-	    {error, transaction_unsupported}
+	    erlang:error(transaction_unsupported)
     end.
 
 -spec sismember(iodata(), iodata()) -> boolean() | redis_error().
@@ -186,7 +192,7 @@ sismember(Set, Member) ->
 		{error, _} = Err -> Err
 	    end;
 	_ ->
-	    {error, transaction_unsupported}
+	    erlang:error(transaction_unsupported)
     end.
 
 -spec scard(iodata()) -> {ok, non_neg_integer()} | redis_error().
@@ -200,7 +206,7 @@ scard(Set) ->
 		    Err
 	    end;
 	_ ->
-	    {error, transaction_unsupported}
+	    erlang:error(transaction_unsupported)
     end.
 
 -spec hget(iodata(), iodata()) -> {ok, undefined | binary()} | redis_error().
@@ -209,7 +215,7 @@ hget(Key, Field) ->
 	undefined ->
 	    q([<<"HGET">>, Key, Field]);
 	_ ->
-	    {error, transaction_unsupported}
+	    erlang:error(transaction_unsupported)
     end.
 
 -spec hset(iodata(), iodata(), iodata()) -> {ok, boolean()} | redis_error() | queued.
@@ -249,7 +255,7 @@ hgetall(Key) ->
 		{error, _} = Err -> Err
 	    end;
 	_ ->
-	    {error, transaction_unsupported}
+	    erlang:error(transaction_unsupported)
     end.
 
 -spec hlen(iodata()) -> {ok, non_neg_integer()} | redis_error().
@@ -261,7 +267,7 @@ hlen(Key) ->
 		{error, _} = Err -> Err
 	    end;
 	_ ->
-	    {error, transaction_unsupported}
+	    erlang:error(transaction_unsupported)
     end.
 
 -spec hkeys(iodata()) -> {ok, [binary()]} | redis_error().
@@ -270,7 +276,7 @@ hkeys(Key) ->
 	undefined ->
 	    q([<<"HKEYS">>, Key]);
 	_ ->
-	    {error, transaction_unsupported}
+	    erlang:error(transaction_unsupported)
     end.
 
 %%%===================================================================
@@ -340,6 +346,7 @@ code_change(_OldVsn, State, _Extra) ->
 %%%===================================================================
 %%% Internal functions
 %%%===================================================================
+-spec connect(state()) -> {ok, pid()} | {error, any()}.
 connect(#state{num = Num}) ->
     Server = ejabberd_config:get_option(redis_server,
 					fun iolist_to_list/1,
@@ -381,9 +388,12 @@ connect(#state{num = Num}) ->
 	    {error, Reason}
     end.
 
--spec call({atom(), atom()}, {q | qp, list()}, integer()) ->
-      {error, disconnected | timeout | binary()} | {ok, iodata()}.
+-spec call({atom(), atom()}, {q, redis_command()}, integer()) ->
+		  {ok, redis_reply()} | redis_error();
+	  ({atom(), atom()}, {qp, redis_pipeline()}, integer()) ->
+		  {ok, [redis_reply()]} | redis_error().
 call({Conn, Parent}, {F, Cmd}, Retries) ->
+    ?DEBUG("redis query: ~p", [Cmd]),
     Res = try eredis:F(Conn, Cmd, ?CALL_TIMEOUT) of
 	      {error, Reason} when is_atom(Reason) ->
 		  try exit(whereis(Conn), kill) catch _:_ -> ok end,
@@ -405,11 +415,14 @@ call({Conn, Parent}, {F, Cmd}, Retries) ->
 	    Res
     end.
 
+-spec get_worker() -> {atom(), atom()}.
 get_worker() ->
     Time = p1_time_compat:system_time(),
     I = erlang:phash2(Time, ejabberd_redis_sup:get_pool_size()) + 1,
     {get_connection(I), get_proc(I)}.
 
+-spec get_result([{error, atom() | binary()} | {ok, iodata()}]) ->
+			{ok, [redis_reply()]} | {error, binary()}.
 get_result([{error, _} = Err|_]) ->
     Err;
 get_result([{ok, _} = OK]) ->
@@ -422,9 +435,11 @@ tr_enq(Cmd, Stack) ->
     erlang:put(?TR_STACK, [Cmd|Stack]),
     queued.
 
+-spec decode_pairs([binary()]) -> [{binary(), binary()}].
 decode_pairs(Pairs) ->
     decode_pairs(Pairs, []).
 
+-spec decode_pairs([binary()], [{binary(), binary()}]) -> [{binary(), binary()}].
 decode_pairs([Field, Val|Pairs], Acc) ->
     decode_pairs(Pairs, [{Field, Val}|Acc]);
 decode_pairs([], Acc) ->
@@ -433,15 +448,18 @@ decode_pairs([], Acc) ->
 dec_bool(<<$1>>) -> true;
 dec_bool(<<$0>>) -> false.
 
+-spec reply(T) -> {ok, T} | queued.
 reply(Val) ->
     case erlang:get(?TR_STACK) of
 	undefined -> {ok, Val};
 	_ -> queued
     end.
 
+-spec iolist_to_list(iodata()) -> string().
 iolist_to_list(IOList) ->
     binary_to_list(iolist_to_binary(IOList)).
 
+-spec max_fsm_queue() -> pos_integer().
 max_fsm_queue() ->
     proplists:get_value(max_queue, fsm_limit_opts(), ?DEFAULT_MAX_QUEUE).
 
@@ -458,6 +476,7 @@ get_queue_type() ->
 	    Type
     end.
 
+-spec flush_queue(p1_queue:queue()) -> p1_queue:queue().
 flush_queue(Q) ->
     CurrTime = p1_time_compat:monotonic_time(milli_seconds),
     p1_queue:dropwhile(
@@ -470,6 +489,7 @@ flush_queue(Q) ->
 	      true
       end, Q).
 
+-spec clean_queue(p1_queue:queue(), integer()) -> p1_queue:queue().
 clean_queue(Q, CurrTime) ->
     Q1 = p1_queue:dropwhile(
 	   fun({_From, Time}) ->