increase session count and ignore table creation errors

WiredTiger session count defaults to 50, but we need at least one per
vnode, so for now hard-code it to 100. Also ignore table creation
results in the kv backend because WiredTiger is currently producing a
strange error if the table already exists.

src/riak_kv_wterl_backend.erl

@@ -92,7 +92,10 @@ start(Partition, Config) ->
                 {ok, ConnRef} ->
                     Table = "table:wt" ++ integer_to_list(Partition),
                     {ok, SRef} = wterl:session_open(ConnRef),
-                    ok = wterl:session_create(SRef, Table),
+                    %% TODO: should check return value here, but we
+                    %% currently get an error when the table already
+                    %% exists, so for now we ignore it.
+                    wterl:session_create(SRef, Table),
                     {ok, #state{conn=ConnRef,
                                 table=Table,
                                 session=SRef,

src/wterl_conn.erl

@@ -69,7 +69,7 @@ init([]) ->
     {ok, #state{}}.
 
 handle_call({open, Dir, Caller}, _From, #state{conn=undefined}=State) ->
-    Opts = [{create, true}, {cache_size, "100MB"}],
+    Opts = [{create, true}, {cache_size, "100MB"}, {session_max, 100}],
     {Reply, NState} = case wterl:conn_open(Dir, wterl:config_to_bin(Opts)) of
                           {ok, ConnRef}=OK ->
                               Monitors = ets:new(?MODULE, []),