Fix pattern-matching index select

src/mrdb_select.erl

@@ -30,6 +30,7 @@
              , limit
              , key_only = false                 % TODO: not used
              , direction = forward
+             , pre_ms
              , derive_obj_f = fun unit_l/1
              }).
 
@@ -51,18 +52,19 @@ select(Ref, MS, AccKeys, Dir, Limit)
     mrdb:with_rdb_iterator(Ref, fun(I) -> i_select(I, Sel, AccKeys, []) end).
 
 mk_sel(#{name := Tab} = Ref, MS, Dir, Limit) ->
-    Keypat = keypat(MS, keypos(Tab), Ref),
+    MSpre = maps:get(pre_ms, Ref, MS),
+    Keypat = keypat(MSpre, keypos(Tab), Ref),
     #sel{tab = Tab,
          ref = Ref,
          keypat = Keypat,
-         ms = MS,
-         compiled_ms = ets:match_spec_compile(MS),
+         ms = MSpre,
+         pre_ms = MSpre,
+         compiled_ms = ms_compile(MS),
          key_only = needs_key_only(MS),
          direction = Dir,
          limit = Limit,
          derive_obj_f = derive_f(Ref)}.
 
-
 select(Cont) ->
     case Cont of
         '$end_of_table' -> '$end_of_table';
@@ -76,6 +78,7 @@ continuation_info(_, _) -> undefined.
 
 continuation_info_(ref,       #sel{ref       = Ref}) -> Ref;
 continuation_info_(ms,        #sel{ms        = MS }) -> MS;
+continuation_info_(pre_ms,    #sel{pre_ms    = MSp}) -> MSp;
 continuation_info_(limit,     #sel{limit     = L  }) -> L;
 continuation_info_(direction, #sel{direction = Dir}) -> Dir;
 continuation_info_(_, _) -> undefined.
@@ -127,7 +130,21 @@ fwd_init_seek_tgt(<<>>  ) -> first;
 fwd_init_seek_tgt(Prefix) -> {seek, Prefix}.
 
 rev_init_seek(I, Pfx) ->
-    rocksdb:iterator_move(I, rev_init_seek_tgt(Pfx)).
+    case rev_init_seek_tgt(Pfx) of
+        last ->
+            i_move(I, last);
+        {seek, Bin} ->
+            %% An 'incremented' prefix.
+            %% This will fail if we seek past the end of the table.
+            %% Then, try to seek_for_prev instead (fails if table empty).
+            %% This because rocksdb lacks a "seek backward to last matching prefix".
+            case i_move(I, {seek, Bin}) of
+                {error, invalid_iterator} ->
+                    i_move(I, {seek_for_prev, Bin});
+                {ok, _, _} = Ok ->
+                    Ok
+            end
+    end.
 
 rev_init_seek_tgt(<<>>) -> last;
 rev_init_seek_tgt(Prefix) ->
@@ -176,19 +193,19 @@ i_select(I, #sel{ keypat = Pfx
                 , limit = Limit
                 , direction = Dir
                 , ref = #{encoding := Enc} } = Sel0, AccKeys, Acc) ->
-    {StartKey, Sel} = case Enc of
-                          {term, _} ->
+    {MoveRes, Sel} = case Enc of
+                         {term, _} ->
                               %% No defined ordering - do forward select
-                              {first, Sel0#sel{direction = forward}};
-                          _ ->
-                              SK = case Dir of
-                                       forward -> fwd_init_seek_tgt(Pfx);
-                                       reverse -> rev_init_seek_tgt(Pfx)
-                                   end,
-                              {SK, Sel0}
-                      end,
-    select_traverse(rocksdb:iterator_move(I, StartKey), Limit,
-                    Pfx, MS, I, Sel, AccKeys, Acc).
+                             {i_move(I, first), Sel0#sel{direction = forward}};
+                         _ ->
+                             case Dir of
+                                 forward ->
+                                     {fwd_init_seek(I, Pfx), Sel0};
+                                 reverse ->
+                                     {rev_init_seek(I, Pfx), Sel0}
+                             end
+                     end,
+    select_traverse(MoveRes, Limit, Pfx, MS, I, Sel, AccKeys, Acc).
 
 needs_key_only([Pat]) ->
     needs_key_only_(Pat);
@@ -271,7 +288,7 @@ select_traverse({ok, K, V}, Limit, Pfx, MS, I, #sel{ref = R, direction = Dir} =
             DecKey = decode_key(K, R),
             Rec0 = decode_val(V, DecKey, R),
             RecL = derive_object(Rec0, Sel),
-            case ets:match_spec_run(RecL, MS) of
+            case ms_run(RecL, MS) of
                 [] ->
                     select_traverse(
                       rocksdb:iterator_move(I, next_or_prev(Dir)), Limit, Pfx, MS,
@@ -340,6 +357,9 @@ iterator_next(I, K, Dir) ->
             Other
     end.
 
+i_move(I, Tgt) ->
+    rocksdb:iterator_move(I, Tgt).
+
 i_move(I, K, reverse) ->
     rocksdb:iterator_move(I, {seek_for_prev, K});
 i_move(I, K, forward) ->
@@ -374,3 +394,9 @@ derive_f(_) -> fun unit_l/1.
 
 unit_l(X) ->
     [X].
+
+ms_compile(MS) ->
+  ets:match_spec_compile(MS).
+
+ms_run(RecL, MS) ->
+    ets:match_spec_run(RecL, MS).