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Tests for fold, fold_reverse, select_reverse, etc.

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This commit is contained in:
Ulf Wiger 2025-06-19 20:12:00 +02:00
parent 323fcea7a7
commit 04e6063ce0
3 changed files with 258 additions and 90 deletions
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45
src/mrdb.erl
View File

@ -66,10 +66,12 @@
, prev/2 , prev/3
, last/1 , last/2
, select/2 , select/3
, select_reverse/2, select_reverse/3
, select/1
, fold/3 , fold/4 , fold/5
, fold_reverse/3 , fold_reverse/4, fold_reverse/5
, rdb_fold/4 , rdb_fold/5
, rdb_rev_fold/4 , rdb_rev_fold/5
, rdb_fold_reverse/4, rdb_fold_reverse/5
, write_info/3
, read_info/2
, read_info/1
@ -541,7 +543,6 @@ re_throw(Cat, Err) ->
throw -> throw(Err)
end.
mnesia_compatible_aborts() ->
mnesia_rocksdb_admin:get_cached_env(mnesia_compatible_aborts, false).
@ -662,10 +663,25 @@ maybe_tx_ctxt([#{activity := #{type := Type} = A} = C|_], R) ->
inherit_ctxt(Ref, R) ->
maps:merge(Ref, maps:with([snapshot, activity], R)).
%% @doc Create an iterator on table `Tab' for the duration of `Fun'
%%
%% The iterator is passed to the provided fun as `Fun(Iterator)', and is
%% closed once the fun terminates.
%% @equiv with_iterator(Tab, Fun, [])
%% @end
-spec with_iterator(ref_or_tab(), fun( (mrdb_iterator()) -> Res )) -> Res.
with_iterator(Tab, Fun) ->
with_iterator(Tab, Fun, []).
%% @doc Create an iterator on table `Tab' with `ReadOptions' for the duration of `Fun'
%%
%% The iterator is passed to the provided fun as `Fun(Iterator)', and is
%% closed once the fun terminates.
%%
%% The iterator respects `mnesia_rocksdb' metadata, so accesses through the iterator
%% will return `{ok, Obj}' where `Obj' is the complete decoded object.
%% For rocksdb-level iterators, see {@link with_rdb_iterator/3}.
%% @end
-spec with_iterator(ref_or_tab(), fun( (mrdb_iterator()) -> Res ), read_options()) -> Res.
with_iterator(Tab, Fun, Opts) ->
R = ensure_ref(Tab),
@ -1301,6 +1317,13 @@ select(Tab, Pat, Limit) when Limit == infinity; is_integer(Limit), Limit > 0 ->
true = valid_limit(Limit),
mrdb_select:select(ensure_ref(Tab), Pat, Limit).
select_reverse(Tab, Pat) ->
select_reverse(Tab, Pat, infinity).
select_reverse(Tab, Pat, Limit) when Limit == infinity; is_integer(Limit), Limit > 0 ->
true = valid_limit(Limit),
mrdb_select:select_reverse(ensure_ref(Tab), Pat, Limit).
select(Cont) ->
mrdb_select:select(Cont).
@ -1355,6 +1378,16 @@ fold(Tab, Fun, Acc, MatchSpec, Limit) ->
true = valid_limit(Limit),
mrdb_select:fold(ensure_ref(Tab), Fun, Acc, MatchSpec, Limit).
fold_reverse(Tab, Fun, Acc) ->
fold_reverse(Tab, Fun, Acc, [{'_', [], ['$_']}]).
fold_reverse(Tab, Fun, Acc, MatchSpec) ->
fold_reverse(Tab, Fun, Acc, MatchSpec, infinity).
fold_reverse(Tab, Fun, Acc, MatchSpec, Limit) ->
true = valid_limit(Limit),
mrdb_select:fold_reverse(ensure_ref(Tab), Fun, Acc, MatchSpec, Limit).
rdb_fold(Tab, Fun, Acc, Prefix) when is_function(Fun, 3)
, is_binary(Prefix) ->
rdb_fold(Tab, Fun, Acc, Prefix, infinity).
@ -1364,14 +1397,14 @@ rdb_fold(Tab, Fun, Acc, Prefix, Limit) when is_function(Fun, 3)
true = valid_limit(Limit),
mrdb_select:rdb_fold(ensure_ref(Tab), Fun, Acc, Prefix, Limit).
rdb_rev_fold(Tab, Fun, Acc, Prefix) when is_function(Fun, 3)
rdb_fold_reverse(Tab, Fun, Acc, Prefix) when is_function(Fun, 3)
, is_binary(Prefix) ->
rdb_rev_fold(Tab, Fun, Acc, Prefix, infinity).
rdb_fold_reverse(Tab, Fun, Acc, Prefix, infinity).
rdb_rev_fold(Tab, Fun, Acc, Prefix, Limit) when is_function(Fun, 3)
rdb_fold_reverse(Tab, Fun, Acc, Prefix, Limit) when is_function(Fun, 3)
, is_binary(Prefix) ->
true = valid_limit(Limit),
mrdb_select:rdb_rev_fold(ensure_ref(Tab), Fun, Acc, Prefix, Limit).
mrdb_select:rdb_fold_reverse(ensure_ref(Tab), Fun, Acc, Prefix, Limit).
valid_limit(L) ->
case L of

114
src/mrdb_select.erl
View File

@ -3,10 +3,13 @@
-export([ select/3 %% (Ref, MatchSpec, Limit)
, select/4 %% (Ref, MatchSpec, AccKeys, Limit)
, select_reverse/3
, select_reverse/4
, select/1 %% (Cont)
, fold/5 %% (Ref, Fun, Acc, MatchSpec, Limit)
, fold_reverse/5
, rdb_fold/5 %% (Ref, Fun, Acc, Prefix, Limit)
, rdb_rev_fold/5 %% (Ref, Fun, Acc, Prefix, Limit)
, rdb_fold_reverse/5 %% (Ref, Fun, Acc, Prefix, Limit)
]).
-export([continuation_info/2]).
@ -26,18 +29,27 @@
, compiled_ms
, limit
, key_only = false % TODO: not used
, direction = forward % TODO: not used
, direction = forward
}).
select(Ref, MS, Limit) when is_map(Ref), is_list(MS) ->
select(Ref, MS, false, Limit).
select(Ref, MS, false, forward, Limit).
select(Ref, MS, AccKeys, Limit)
select(Ref, MS, AccKeys, Limit) ->
select(Ref, MS, AccKeys, forward, Limit).
select_reverse(Ref, MS, Limit) ->
select(Ref, MS, false, reverse, Limit).
select_reverse(Ref, MS, AccKeys, Limit) ->
select(Ref, MS, AccKeys, reverse, Limit).
select(Ref, MS, AccKeys, Dir, Limit)
when is_map(Ref), is_list(MS), is_boolean(AccKeys) ->
Sel = mk_sel(Ref, MS, Limit),
Sel = mk_sel(Ref, MS, Dir, Limit),
mrdb:with_rdb_iterator(Ref, fun(I) -> i_select(I, Sel, AccKeys, []) end).
mk_sel(#{name := Tab} = Ref, MS, Limit) ->
mk_sel(#{name := Tab} = Ref, MS, Dir, Limit) ->
Keypat = keypat(MS, keypos(Tab), Ref),
#sel{tab = Tab,
ref = Ref,
@ -45,6 +57,7 @@ mk_sel(#{name := Tab} = Ref, MS, Limit) ->
ms = MS,
compiled_ms = ets:match_spec_compile(MS),
key_only = needs_key_only(MS),
direction = Dir,
limit = Limit}.
select(Cont) ->
@ -65,6 +78,12 @@ continuation_info_(direction, #sel{direction = Dir}) -> Dir;
continuation_info_(_, _) -> undefined.
fold(Ref, Fun, Acc, MS, Limit) ->
do_fold(Ref, Fun, Acc, MS, forward, Limit).
fold_reverse(Ref, Fun, Acc, MS, Limit) ->
do_fold(Ref, Fun, Acc, MS, reverse, Limit).
do_fold(Ref, Fun, Acc, MS, Dir, Limit) ->
{AccKeys, F} =
if is_function(Fun, 3) ->
{true, fun({K, Obj}, Acc1) ->
@ -75,7 +94,7 @@ fold(Ref, Fun, Acc, MS, Limit) ->
true ->
mrdb:abort(invalid_fold_fun)
end,
fold_(select(Ref, MS, AccKeys, Limit), F, Acc).
fold_(select(Ref, MS, AccKeys, Dir, Limit), F, Acc).
fold_('$end_of_table', _, Acc) ->
Acc;
@ -91,27 +110,29 @@ rdb_fold(Ref, Fun, Acc, Prefix, Limit) ->
i_rdb_fold(MovRes, I, Prefix, Fun, Acc, Limit)
end).
rdb_rev_fold(Ref, Fun, Acc, Prefix, Limit) ->
rdb_fold_reverse(Ref, Fun, Acc, Prefix, Limit) ->
mrdb:with_rdb_iterator(
Ref, fun(I) ->
MovRes = rev_init_seek(I, Prefix),
i_rdb_rev_fold(MovRes, I, Prefix, Fun, Acc, Limit)
i_rdb_fold_reverse(MovRes, I, Prefix, Fun, Acc, Limit)
end).
fwd_init_seek(I, <<>>) ->
rocksdb:iterator_move(I, first);
fwd_init_seek(I, Prefix) ->
rocksdb:iterator_move(I, {seek, Prefix}).
fwd_init_seek(I, Pfx) ->
rocksdb:iterator_move(I, fwd_init_seek_tgt(Pfx)).
rev_init_seek(I, <<>>) ->
rocksdb:iterator_move(I, last);
rev_init_seek(I, Prefix) ->
Tgt = case incr_prefix(Prefix) of
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)).
rev_init_seek_tgt(<<>>) -> last;
rev_init_seek_tgt(Prefix) ->
case incr_prefix(Prefix) of
last -> last;
Pfx1 when is_binary(Pfx1) ->
{seek, Pfx1}
end,
rocksdb:iterator_move(I, Tgt).
end.
incr_prefix(<<>>) -> last;
incr_prefix(Pfx) when is_binary(Pfx) ->
@ -134,30 +155,34 @@ i_rdb_fold({ok, K, V}, I, Pfx, Fun, Acc, Limit) when Limit > 0 ->
i_rdb_fold(_, _, _, _, Acc, _) ->
Acc.
i_rdb_rev_fold({ok, K, V}, I, Pfx, Fun, Acc, Limit) when Limit > 0 ->
i_rdb_fold_reverse({ok, K, V}, I, Pfx, Fun, Acc, Limit) when Limit > 0 ->
case is_prefix(Pfx, K) of
true ->
i_rdb_rev_fold(rocksdb:iterator_move(I, prev), I, Pfx, Fun,
i_rdb_fold_reverse(rocksdb:iterator_move(I, prev), I, Pfx, Fun,
Fun(K, V, Acc), decr(Limit));
false when K > Pfx ->
i_rdb_rev_fold(rocksdb:iterator_move(I, prev), I, Pfx, Fun, Acc, Limit);
i_rdb_fold_reverse(rocksdb:iterator_move(I, prev), I, Pfx, Fun, Acc, Limit);
false ->
Acc
end;
i_rdb_rev_fold(_, _, _, _, Acc, _) ->
i_rdb_fold_reverse(_, _, _, _, Acc, _) ->
Acc.
i_select(I, #sel{ keypat = Pfx
, compiled_ms = MS
, limit = Limit
, ref = #{vsn := Vsn, encoding := Enc} } = Sel, AccKeys, Acc) ->
StartKey = case {Pfx, Vsn, Enc} of
{<<>>, 1, {sext, _}} ->
<<?DATA_START>>;
{_, _, {term, _}} ->
<<>>;
, direction = Dir
, ref = #{encoding := Enc} } = Sel0, AccKeys, Acc) ->
{StartKey, Sel} = case Enc of
{term, _} ->
%% No defined ordering - do forward select
{first, Sel0#sel{direction = forward}};
_ ->
Pfx
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).
@ -236,7 +261,7 @@ map_vars([H|T], P) ->
map_vars([], _) ->
[].
select_traverse({ok, K, V}, Limit, Pfx, MS, I, #sel{ref = R} = Sel,
select_traverse({ok, K, V}, Limit, Pfx, MS, I, #sel{ref = R, direction = Dir} = Sel,
AccKeys, Acc) ->
case is_prefix(Pfx, K) of
true ->
@ -245,7 +270,7 @@ select_traverse({ok, K, V}, Limit, Pfx, MS, I, #sel{ref = R} = Sel,
case ets:match_spec_run([Rec], MS) of
[] ->
select_traverse(
rocksdb:iterator_move(I, next), Limit, Pfx, MS,
rocksdb:iterator_move(I, next_or_prev(Dir)), Limit, Pfx, MS,
I, Sel, AccKeys, Acc);
[Match] ->
Acc1 = if AccKeys ->
@ -255,6 +280,9 @@ select_traverse({ok, K, V}, Limit, Pfx, MS, I, #sel{ref = R} = Sel,
end,
traverse_continue(K, decr(Limit), Pfx, MS, I, Sel, AccKeys, Acc1)
end;
false when Dir == reverse, K > Pfx ->
select_traverse(rocksdb:iterator_move(I, prev), Limit, Pfx, MS,
I, Sel, AccKeys, Acc);
false when Limit == infinity ->
lists:reverse(Acc);
false ->
@ -263,6 +291,9 @@ select_traverse({ok, K, V}, Limit, Pfx, MS, I, #sel{ref = R} = Sel,
select_traverse({error, _}, Limit, _, _, _, _, _, Acc) ->
select_return(Limit, {lists:reverse(Acc), '$end_of_table'}).
next_or_prev(forward) -> next;
next_or_prev(reverse) -> prev.
select_return(infinity, {L, '$end_of_table'}) ->
L;
select_return(_, Ret) ->
@ -282,29 +313,34 @@ decr(I) when is_integer(I) ->
decr(infinity) ->
infinity.
traverse_continue(K, 0, Pfx, MS, _I, #sel{limit = Limit, ref = Ref} = Sel, AccKeys, Acc) ->
traverse_continue(K, 0, Pfx, MS, _I, #sel{limit = Limit, ref = Ref, direction = Dir} = Sel, AccKeys, Acc) ->
{lists:reverse(Acc),
fun(sel) -> Sel;
(cont) ->
mrdb:with_rdb_iterator(
Ref,
fun(NewI) ->
select_traverse(iterator_next(NewI, K),
select_traverse(iterator_next(NewI, K, Dir),
Limit, Pfx, MS, NewI, Sel,
AccKeys, [])
end)
end};
traverse_continue(_K, Limit, Pfx, MS, I, Sel, AccKeys, Acc) ->
select_traverse(rocksdb:iterator_move(I, next), Limit, Pfx, MS, I, Sel, AccKeys, Acc).
traverse_continue(_K, Limit, Pfx, MS, I, #sel{direction = Dir} = Sel, AccKeys, Acc) ->
select_traverse(rocksdb:iterator_move(I, next_or_prev(Dir)), Limit, Pfx, MS, I, Sel, AccKeys, Acc).
iterator_next(I, K) ->
case rocksdb:iterator_move(I, K) of
iterator_next(I, K, Dir) ->
case i_move(I, K, Dir) of
{ok, K, _} ->
rocksdb:iterator_move(I, next);
rocksdb:iterator_move(I, next_or_prev(Dir));
Other ->
Other
end.
i_move(I, K, reverse) ->
rocksdb:iterator_move(I, {seek_for_prev, K});
i_move(I, K, forward) ->
rocksdb:iterator_move(I, K).
keypat([H|T], KeyPos, Ref) ->
keypat(T, KeyPos, Ref, keypat_pfx(H, KeyPos, Ref)).

161
test/mrdb_fold_SUITE.erl
View File

@ -12,15 +12,26 @@
, end_per_testcase/2
]).
-export([ no_prefix_fwd_rdb_fold/1
-export([
no_prefix_fwd_rdb_fold/1
, prefixed_fwd_rdb_fold/1
, no_prefix_rev_rdb_fold/1
, prefixed_rev_rdb_fold/1
, prefixed_rev_rdb_fold_max/1
, fwd_fold/1
, filtered_fwd_fold/1
, rev_fold/1
, filtered_rev_fold/1
, fwd_select/1
, rev_select/1
, select_cont/1
, rev_select_cont/1
]).
-include_lib("common_test/include/ct.hrl").
-record(r, {k, v}).
suite() ->
[].
@ -29,26 +40,37 @@ all() ->
groups() ->
[
{all_tests, [sequence], [ {group, rdb_fwd_fold}
, {group, rdb_rev_fold} ]}
, {rdb_fwd_fold, [sequence], [ no_prefix_fwd_rdb_fold
, prefixed_fwd_rdb_fold ]}
, {rdb_rev_fold, [sequence], [ no_prefix_rev_rdb_fold
{all_tests, [sequence], [ {group, rdb_fold}
, {group, fold}
, {group, select} ]}
, {rdb_fold, [sequence], [ no_prefix_fwd_rdb_fold
, prefixed_fwd_rdb_fold
, no_prefix_rev_rdb_fold
, prefixed_rev_rdb_fold
, prefixed_rev_rdb_fold_max ]}
, {fold, [sequence], [ fwd_fold
, filtered_fwd_fold
, rev_fold
, filtered_rev_fold ]}
, {select, [sequence], [ fwd_select
, rev_select
, select_cont
, rev_select_cont ]}
].
init_per_suite(Config) ->
mnesia:stop(),
ok = mnesia_rocksdb_tlib:start_mnesia(reset),
Config.
end_per_suite(_Config) ->
mnesia:stop(),
ok.
init_per_group(G, Config) ->
mnesia:stop(),
ok = mnesia_rocksdb_tlib:start_mnesia(reset),
create_tab(t, G, [{type, ordered_set}]),
fill_tab(t),
init_per_group(G, Config) when G==rdb_fold; G==fold ->
mk_tab(G),
Config;
init_per_group(_, Config) ->
Config.
end_per_group(_, _Config) ->
@ -60,62 +82,139 @@ init_per_testcase(_, Config) ->
end_per_testcase(_, _Config) ->
ok.
create_tab(Tab, Grp, Opts) ->
GOpts = case Grp of
_ when Grp==rdb_fwd_fold; Grp==rdb_rev_fold ->
[{user_properties,
[{mrdb_encoding, {raw, raw}}]}];
_ -> []
end,
{atomic, ok} = mnesia:create_table(Tab, [{rdb, [node()]} | GOpts ++ Opts]),
ok.
mk_tab(G) ->
T = tab_name(G),
case create_tab(T) of
{atomic, ok} -> fill_tab(T);
{aborted,{already_exists,T}} -> ok
end.
tab_name(fold ) -> r;
tab_name(select ) -> r;
tab_name(rdb_fold) -> t.
create_tab(T) ->
Opts = tab_opts(T),
mnesia:create_table(T, [{rdb, [node()]} | Opts]).
tab_opts(r) ->
[{attributes, [k, v]}, {type, ordered_set}];
tab_opts(t) ->
[{attributes, [k, v]}, {user_properties, [{mrdb_encoding, {raw, raw}}]}].
no_prefix_fwd_rdb_fold(_Config) ->
Res = mrdb:rdb_fold(t, fun simple_rdb_acc/3, [], <<>>, infinity),
Expected = lists:reverse(raw_objs()),
{Res, Res} = {Res, Expected}.
fwd_fold(_Config) ->
Res = mrdb:fold(r, fun simple_acc/2, []),
Expected = lists:reverse(objs()),
{Res, Res} = {Res, Expected}.
prefixed_fwd_rdb_fold(_Config) ->
Pfx = <<"aa">>,
Res = mrdb:rdb_fold(t, fun simple_rdb_acc/3, [], Pfx, infinity),
Expected = lists:reverse(prefixed_objs(Pfx)),
Expected = lists:reverse(prefixed_raw_objs(Pfx)),
{Res, Res} = {Res, Expected}.
filtered_fwd_fold(_Config) ->
MS = [{#r{k = {a,b,'_'}, v = '_'}, [], ['$_']}],
Res = mrdb:fold(r, fun simple_acc/2, [], MS, infinity),
Expected = lists:reverse(filtered_objs(MS)),
{Res, Res} = {Res, Expected}.
no_prefix_rev_rdb_fold(_Config) ->
Res = mrdb:rdb_rev_fold(t, fun simple_rdb_acc/3, [], <<>>, infinity),
Res = mrdb:rdb_fold_reverse(t, fun simple_rdb_acc/3, [], <<>>, infinity),
Expected = raw_objs(),
{Res, Res} = {Res, Expected}.
rev_fold(_Config) ->
Res = mrdb:fold_reverse(r, fun simple_acc/2, []),
Expected = objs(),
{Res, Res} = {Res, Expected}.
prefixed_rev_rdb_fold(_Config) ->
Pfx = <<"aa">>,
Res = mrdb:rdb_rev_fold(t, fun simple_rdb_acc/3, [], Pfx, infinity),
Expected = prefixed_objs(Pfx),
Res = mrdb:rdb_fold_reverse(t, fun simple_rdb_acc/3, [], Pfx, infinity),
Expected = prefixed_raw_objs(Pfx),
{Res, Res} = {Res, Expected}.
filtered_rev_fold(_Config) ->
MS = [{#r{k = {a,b,'_'}, v = '_'}, [], ['$_']}],
Res = mrdb:fold_reverse(r, fun simple_acc/2, [], MS, infinity),
Expected = filtered_objs(MS),
{Res, Res} = {Res, Expected}.
prefixed_rev_rdb_fold_max(_Config) ->
Pfx = <<255,255>>,
Res = mrdb:rdb_rev_fold(t, fun simple_rdb_acc/3, [], Pfx, infinity),
Expected = prefixed_objs(Pfx),
Res = mrdb:rdb_fold_reverse(t, fun simple_rdb_acc/3, [], Pfx, infinity),
Expected = prefixed_raw_objs(Pfx),
{Res, Res} = {Res, Expected}.
fwd_select(_Config) ->
MS = [{#r{k = {a,b,'_'}, v = '_'}, [], ['$_']}],
Res = mrdb:select(r, MS),
Expected = filtered_objs(MS),
{Res, Res} = {Res, Expected}.
rev_select(_Config) ->
MS = [{#r{k = {a,b,'_'}, v = '_'}, [], ['$_']}],
Res = mrdb:select_reverse(r, MS),
Expected = lists:reverse(filtered_objs(MS)),
{Res, Res} = {Res, Expected}.
select_cont(_Cont) ->
MS = [{#r{k = {a,b,'_'}, v = '_'}, [], ['$_']}],
Expected = filtered_objs(MS),
select_cont_loop(mrdb:select(r, MS, 1), Expected).
rev_select_cont(_Cont) ->
MS = [{#r{k = {a,b,'_'}, v = '_'}, [], ['$_']}],
Expected = lists:reverse(filtered_objs(MS)),
select_cont_loop(mrdb:select_reverse(r, MS, 1), Expected).
select_cont_loop({[Obj], Cont}, [Obj|Rest]) ->
select_cont_loop(mrdb:select(Cont), Rest);
select_cont_loop({[], '$end_of_table'}, []) ->
ok.
simple_acc(#r{} = Obj, Acc) ->
[Obj | Acc].
simple_rdb_acc(K, V, Acc) ->
[{K,V} | Acc].
fill_tab(Tab) ->
[mrdb:insert(Tab, {Tab, K, V}) || {K,V} <- objs()],
fill_tab(t = Tab) ->
[mrdb:insert(Tab, {Tab, K, V}) || {K,V} <- raw_objs()],
ok;
fill_tab(r = Tab) ->
[mrdb:insert(Tab, Obj) || Obj <- objs()],
ok.
prefixed_objs(Pfx) ->
[Obj || {K,_} = Obj <- objs(),
prefixed_raw_objs(Pfx) ->
[Obj || {K,_} = Obj <- raw_objs(),
is_prefix(Pfx, K)].
objs() ->
raw_objs() ->
[ {<<"aa">> , <<"1">>}
, {<<"aa1">>, <<"2">>}
, {<<"ab">> , <<"3">>}
, {<<"ab1">>, <<"4">>}
, {<<255,255>>, <<"5">>} ].
filtered_objs(MS) ->
MSC = ets:match_spec_compile(MS),
ets:match_spec_run(objs(), MSC).
objs() ->
[ #r{k = {a,a,1}, v = 1}
, #r{k = {a,b,2}, v = 2}
, #r{k = {a,b,3}, v = 3}
, #r{k = {a,c,4}, v = 4}
, #r{k = {b,b,5}, v = 5}
].
%% copied from mrdb_select.erl
is_prefix(A, B) when is_binary(A), is_binary(B) ->
Sa = byte_size(A),