Mas d34 ms.i446 plusplus (#448)

* Minor optimisations

Try to reduce the calls to ++, and ensure that where possible the shorted list is being copied.

* Pass Acc into function

So that the list can be accumulated efficiently, without an additional copy to add back the accumulator at the end.

* prepend to accumulators

Code review to make sure we prepend to accumulators everywhere, to reduce the copying involved.

attempt to further optimise in leveled_sst (where most expensive ++ occurs).  This optimises for the case when Acc is [], and enforces a series of '++' to start from the right, prepending in turn.  Some shell testing indicated that this was not necessarily the case (although this doesn't seem tobe consistently reproducible).

```
6> element(1, timer:tc(fun() -> KL1 ++ KL2 ++ KL3 ++ KL4 end)).
28
7> element(1, timer:tc(fun() -> KL1 ++ KL2 ++ KL3 ++ KL4 end)).
174
8> element(1, timer:tc(fun() -> KL1 ++ KL2 ++ KL3 ++ KL4 end)).
96
9> element(1, timer:tc(fun() -> KL1 ++ KL2 ++ KL3 ++ KL4 end)).
106
10> element(1, timer:tc(fun() -> KL1 ++ KL2 ++ KL3 ++ KL4 end)).
112

17> element(1, timer:tc(fun() -> lists:foldr(fun(KL0, KLAcc) -> KL0 ++ KLAcc end, [], [KL1, KL2, KL3, KL4]) end)).
21
18> element(1, timer:tc(fun() -> lists:foldr(fun(KL0, KLAcc) -> KL0 ++ KLAcc end, [], [KL1, KL2, KL3, KL4]) end)).
17
19> element(1, timer:tc(fun() -> lists:foldr(fun(KL0, KLAcc) -> KL0 ++ KLAcc end, [], [KL1, KL2, KL3, KL4]) end)).
12
20> element(1, timer:tc(fun() -> lists:foldr(fun(KL0, KLAcc) -> KL0 ++ KLAcc end, [], [KL1, KL2, KL3, KL4]) end)).
11
```

running eprof indicates that '++' and lists:reverse have been reduced (however impact had only previously been 1-2%)

* Add unit test to confirm (limited) merit of optimised list function

No difference in unit test with/without inline compilation, so this has been removed

* Update src/leveled_sst.erl

These functions had previously used inline compilation - but this didn't appear to improve performance

Co-authored-by: Thomas Arts <thomas.arts@quviq.com>

* Update src/leveled_sst.erl

Co-authored-by: Thomas Arts <thomas.arts@quviq.com>

* Update src/leveled_ebloom.erl

Co-authored-by: Thomas Arts <thomas.arts@quviq.com>

* Update following review

Also fix code coverage issues

* Update src/leveled_sst.erl

Co-authored-by: Thomas Arts <thomas.arts@quviq.com>

---------

Co-authored-by: Thomas Arts <thomas.arts@quviq.com>

src/leveled_cdb.erl

@@ -1722,11 +1722,11 @@ build_hashtree_binary(SlotMap, IndexLength) ->
 
 build_hashtree_binary([], IdxLen, SlotPos, Bin) ->
     case SlotPos of
-        IdxLen ->
+        N when N == IdxLen ->
-            lists:reverse(Bin);
+            Bin;
         N when N < IdxLen ->
             ZeroLen = (IdxLen - N) * 64,
-            lists:reverse([<<0:ZeroLen>>|Bin])
+            [<<0:ZeroLen>>|Bin]
     end;
 build_hashtree_binary([{TopSlot, TopBin}|SlotMapTail], IdxLen, SlotPos, Bin) ->
     case TopSlot of
@@ -1774,7 +1774,7 @@ write_hash_tables([], _HashTree, _CurrPos, _BasePos,
                                         IndexList, HT_BinList, {T1, T2, T3}) ->
     leveled_log:log(cdb14, [T1, T2, T3]),
     IL = lists:reverse(IndexList),
-    {IL, list_to_binary(HT_BinList)};
+    {IL, list_to_binary(lists:reverse(HT_BinList))};
 write_hash_tables([Index|Rest], HashTree, CurrPos, BasePos,
                                         IndexList, HT_BinList, Timers) ->
     SW1 = os:timestamp(),
@@ -1782,13 +1782,15 @@ write_hash_tables([Index|Rest], HashTree, CurrPos, BasePos,
     T1 = timer:now_diff(os:timestamp(), SW1) + element(1, Timers),
     case SlotMap of
         [] ->
-            write_hash_tables(Rest,
+            write_hash_tables(
+                Rest,
                 HashTree,
                 CurrPos,
                 BasePos,
                 [{Index, BasePos, 0}|IndexList],
                 HT_BinList,
-                                Timers);
+                Timers
+            );
         _ ->
             SW2 = os:timestamp(),
             IndexLength = length(SlotMap) * 2,
@@ -1797,13 +1799,15 @@ write_hash_tables([Index|Rest], HashTree, CurrPos, BasePos,
             SW3 = os:timestamp(),
             NewSlotBin = build_hashtree_binary(SortedMap, IndexLength),
             T3 = timer:now_diff(os:timestamp(), SW3) + element(3, Timers),
-            write_hash_tables(Rest,
+            write_hash_tables(
+                Rest,
                 HashTree,
                 CurrPos + IndexLength * ?DWORD_SIZE,
                 BasePos,
                 [{Index, CurrPos, IndexLength}|IndexList],
-                                HT_BinList ++ NewSlotBin,
+                lists:append(NewSlotBin, HT_BinList),
-                                {T1, T2, T3})
+                {T1, T2, T3}
+            )
     end.
 
 
@@ -1949,7 +1953,12 @@ build_hashtree_bunchedatend_binary_test() ->
                 {14, <<15:32, 500:32>>},
                 {15, <<16:32, 600:32>>},
                 {15, <<17:32, 700:32>>}],
-    Bin = list_to_binary(build_hashtree_binary(SlotMap, 16)),
+    Bin =
+        list_to_binary(
+            lists:reverse(
+                build_hashtree_binary(SlotMap, 16)
+            )
+        ),
     ExpBinP1 = <<16:32, 600:32, 10:32, 0:32, 17:32, 700:32, 0:64>>,
     ExpBinP2 = <<11:32, 100:32, 0:192, 12:32, 200:32, 13:32, 300:32, 0:256>>,
     ExpBinP3 = <<14:32, 400:32, 15:32, 500:32>>,
@@ -1965,7 +1974,12 @@ build_hashtree_bunchedatstart_binary_test() ->
                 {6, <<15:32, 500:32>>},
                 {7, <<16:32, 600:32>>},
                 {8, <<17:32, 700:32>>}],
-    Bin = list_to_binary(build_hashtree_binary(SlotMap, 16)),
+    Bin =
+        list_to_binary(
+            lists:reverse(
+                build_hashtree_binary(SlotMap, 16)
+            )
+        ),
     ExpBinP1 = <<0:64, 10:32, 0:32, 11:32, 100:32, 12:32, 200:32>>,
     ExpBinP2 = <<13:32, 300:32, 14:32, 400:32, 15:32, 500:32, 16:32, 600:32>>,
     ExpBinP3 = <<17:32, 700:32, 0:448>>,
@@ -1988,7 +2002,7 @@ build_hashtree_test() ->
                 [<<2424915712:32, 300:32>>, <<0:64>>] ++
                 [<<2424903936:32, 400:32>>, <<2424907008:32, 500:32>>] ++
                 [<<2424913408:32, 600:32>>],
-    ?assertMatch(ExpOut, BinList).
+    ?assertMatch(ExpOut, lists:reverse(BinList)).
 
 
 find_firstzero_test() ->

src/leveled_ebloom.erl

@@ -92,11 +92,11 @@ check_hash({_SegHash, Hash}, BloomBin) when is_binary(BloomBin)->
 map_hashes([], HashListTuple,  _SlotCount) ->
     HashListTuple;
 map_hashes([Hash|Rest], HashListTuple, SlotCount) ->
-    {Slot, Hashes} = split_hash(element(2, Hash), SlotCount),
+    {Slot, [H0, H1]} = split_hash(element(2, Hash), SlotCount),
     SlotHL = element(Slot + 1, HashListTuple),
     map_hashes(
         Rest,
-        setelement(Slot + 1, HashListTuple, Hashes ++ SlotHL),
+        setelement(Slot + 1, HashListTuple, [H0, H1 | SlotHL]),
         SlotCount).
 
 -spec split_hash(external_hash(), slot_count())

src/leveled_head.erl

@@ -421,8 +421,8 @@ decode_maybe_binary(<<0, Bin/binary>>) ->
 decode_maybe_binary(<<_Other:8, Bin/binary>>) ->
     Bin.
 
--spec diff_index_data([{binary(), index_value()}],
+-spec diff_index_data(
-                      [{binary(), index_value()}]) ->
+    [{binary(), index_value()}], [{binary(), index_value()}]) ->
         [{index_op(), binary(), index_value()}].
 diff_index_data(OldIndexes, AllIndexes) ->
     OldIndexSet = ordsets:from_list(OldIndexes),
@@ -435,17 +435,19 @@ diff_specs_core(AllIndexSet, OldIndexSet) ->
     RemoveIndexSet =
         ordsets:subtract(OldIndexSet, AllIndexSet),
     NewIndexSpecs =
-        assemble_index_specs(ordsets:subtract(NewIndexSet, OldIndexSet),
+        assemble_index_specs(
-                             add),
+            ordsets:subtract(NewIndexSet, OldIndexSet),
+            add
+        ),
     RemoveIndexSpecs =
-        assemble_index_specs(RemoveIndexSet,
+        assemble_index_specs(RemoveIndexSet, remove),
-                             remove),
     NewIndexSpecs ++ RemoveIndexSpecs.
 
 %% @doc Assemble a list of index specs in the
 %% form of triplets of the form
 %% {IndexOperation, IndexField, IndexValue}.
--spec assemble_index_specs([{binary(), binary()}], index_op()) ->
+-spec assemble_index_specs(
+    [{binary(), binary()}], index_op()) ->
         [{index_op(), binary(), binary()}].
 assemble_index_specs(Indexes, IndexOp) ->
     [{IndexOp, Index, Value} || {Index, Value} <- Indexes].

src/leveled_pclerk.erl

@@ -217,10 +217,13 @@ merge(SrcLevel, Manifest, RootPath, OptsSST) ->
     Src =
         leveled_pmanifest:mergefile_selector(Manifest, SrcLevel, SelectMethod),
     NewSQN = leveled_pmanifest:get_manifest_sqn(Manifest) + 1,
-    SinkList = leveled_pmanifest:merge_lookup(Manifest,
+    SinkList =
+        leveled_pmanifest:merge_lookup(
+            Manifest,
             SrcLevel + 1,
             Src#manifest_entry.start_key,
-                                                Src#manifest_entry.end_key),
+            Src#manifest_entry.end_key
+        ),
     Candidates = length(SinkList),
     leveled_log:log(pc008, [SrcLevel, Candidates]),
     case Candidates of
@@ -228,10 +231,13 @@ merge(SrcLevel, Manifest, RootPath, OptsSST) ->
             NewLevel = SrcLevel + 1,
             leveled_log:log(pc009, [Src#manifest_entry.filename, NewLevel]),
             leveled_sst:sst_switchlevels(Src#manifest_entry.owner, NewLevel),
-            Man0 = leveled_pmanifest:switch_manifest_entry(Manifest,
+            Man0 =
+                leveled_pmanifest:switch_manifest_entry(
+                    Manifest,
                     NewSQN,
                     SrcLevel,
-                                                            Src),
+                    Src
+                ),
             {Man0, []};
         _ ->
             SST_RP = leveled_penciller:sst_rootpath(RootPath),
@@ -253,44 +259,50 @@ notify_deletions([Head|Tail], Penciller) ->
 %%
 %% SrcLevel is the level of the src sst file, the sink should be srcLevel + 1
 
-perform_merge(Manifest, 
+perform_merge(Manifest, Src, SinkList, SrcLevel, RootPath, NewSQN, OptsSST) ->
-                Src, SinkList, SrcLevel, 
-                RootPath, NewSQN, 
-                OptsSST) ->
     leveled_log:log(pc010, [Src#manifest_entry.filename, NewSQN]),
     SrcList = [{next, Src, all}],
     MaxSQN = leveled_sst:sst_getmaxsequencenumber(Src#manifest_entry.owner),
     SinkLevel = SrcLevel + 1,
     SinkBasement = leveled_pmanifest:is_basement(Manifest, SinkLevel),
     Additions = 
-        do_merge(SrcList, SinkList,
+        do_merge(
+            SrcList, SinkList,
             SinkLevel, SinkBasement,
             RootPath, NewSQN, MaxSQN,
             OptsSST,
-                    []),
+            []
+        ),
     RevertPointerFun =
         fun({next, ME, _SK}) ->
             ME
         end,
     SinkManifestList = lists:map(RevertPointerFun, SinkList),
-    Man0 = leveled_pmanifest:replace_manifest_entry(Manifest,
+    Man0 =
+        leveled_pmanifest:replace_manifest_entry(
+            Manifest,
             NewSQN,
             SinkLevel,
             SinkManifestList,
-                                                    Additions),
+            Additions
-    Man2 = leveled_pmanifest:remove_manifest_entry(Man0,
+        ),
+    Man2 =
+        leveled_pmanifest:remove_manifest_entry(
+            Man0,
             NewSQN,
             SrcLevel,
-                                                    Src),
+            Src
+        ),
     {Man2, [Src|SinkManifestList]}.
 
 do_merge([], [], SinkLevel, _SinkB, _RP, NewSQN, _MaxSQN, _Opts, Additions) ->
     leveled_log:log(pc011, [NewSQN, SinkLevel, length(Additions)]),
-    Additions;
+    lists:reverse(Additions);
 do_merge(KL1, KL2, SinkLevel, SinkB, RP, NewSQN, MaxSQN, OptsSST, Additions) ->
-    FileName = leveled_penciller:sst_filename(NewSQN,
+    FileName =
-                                                SinkLevel,
+        leveled_penciller:sst_filename(
-                                                length(Additions)),
+            NewSQN, SinkLevel, length(Additions)
+        ),
     leveled_log:log(pc012, [NewSQN, FileName, SinkB]),
     TS1 = os:timestamp(),
     case leveled_sst:sst_newmerge(RP, FileName,
@@ -298,24 +310,31 @@ do_merge(KL1, KL2, SinkLevel, SinkB, RP, NewSQN, MaxSQN, OptsSST, Additions) ->
                                     OptsSST) of
         empty ->
             leveled_log:log(pc013, [FileName]),
-            do_merge([], [],
+            do_merge(
+                [], [],
                 SinkLevel, SinkB,
                 RP, NewSQN, MaxSQN,
                 OptsSST, 
-                        Additions);                        
+                Additions
+            );                        
         {ok, Pid, Reply, Bloom} ->
             {{KL1Rem, KL2Rem}, SmallestKey, HighestKey} = Reply,
-                Entry = #manifest_entry{start_key=SmallestKey,
+                Entry =
+                    #manifest_entry{
+                        start_key=SmallestKey,
                         end_key=HighestKey,
                         owner=Pid,
                         filename=FileName,
-                                            bloom=Bloom},
+                        bloom=Bloom
+                    },
                 leveled_log:log_timer(pc015, [], TS1),
-                do_merge(KL1Rem, KL2Rem,
+                do_merge(
+                    KL1Rem, KL2Rem,
                     SinkLevel, SinkB,
                     RP, NewSQN, MaxSQN,
                     OptsSST,
-                            Additions ++ [Entry])
+                    [Entry|Additions]
+                )
     end.
 
 -spec grooming_scorer(

src/leveled_penciller.erl

@@ -2002,6 +2002,9 @@ format_status_test() ->
     ?assertMatch(redacted, ST#state.levelzero_cache),
     ?assertMatch(redacted, ST#state.levelzero_index),
     ?assertMatch(redacted, ST#state.levelzero_astree),
+    NormStatus = format_status(#{reason => normal, state => S}),
+    NST = maps:get(state, NormStatus),
+    ?assert(is_integer(array:size(element(2, NST#state.manifest)))),
     clean_testdir(RootPath).
 
 close_no_crash_test_() ->

src/leveled_sst.erl

@@ -57,7 +57,6 @@
 %% the transaction log replay; or by using a higher level for of anti-entropy
 %% (i.e. make Riak responsible).
 
-
 -module(leveled_sst).
 
 -behaviour(gen_statem).
@@ -1395,41 +1394,28 @@ fetch(LedgerKey, Hash,
 %% Fetch pointers to the slots the SST file covered by a given key range.
 fetch_range(StartKey, EndKey, Summary, FilterFun, true) ->
     {Slots, RTrim} =
-        lookup_slots(
+        lookup_slots(StartKey, EndKey, Summary#summary.index, FilterFun),
-            StartKey,
-            EndKey,
-            Summary#summary.index,
-            FilterFun),
     Self = self(),
-    SL = length(Slots),
+    case {Slots, if not RTrim -> all; RTrim -> EndKey end} of
-    case SL of
+        {[Slot], LastKey} ->
-        1 ->
+            [{pointer, Self, Slot, StartKey, LastKey}];
-            [Slot] = Slots,
+        {[Hd|Rest], all} ->
-            case RTrim of
+            RightPointers =
-                true ->
+                lists:map(
-                    [{pointer, Self, Slot, StartKey, EndKey}];
+                    fun(S) -> {pointer, Self, S, all, all} end,
-                false ->
+                    Rest),
-                    [{pointer, Self, Slot, StartKey, all}]
+            [{pointer, Self, Hd, StartKey, all}|RightPointers];
-            end;
+        {[Hd|Rest], LastKey} ->
-        N ->
+            {MidSlots, [Last]} = lists:split(length(Rest) - 1, Rest),
-            {LSlot, MidSlots, RSlot} =
-                {hd(Slots), lists:sublist(Slots, 2, N - 2), lists:last(Slots)},
             MidSlotPointers =
                 lists:map(
                     fun(S) -> {pointer, Self, S, all, all} end,
                     MidSlots),
-            case RTrim of
+            [{pointer, Self, Hd, StartKey, all}|MidSlotPointers]
-                true ->
+                ++ [{pointer, Self, Last, all, LastKey}]
-                    [{pointer, Self, LSlot, StartKey, all}] ++
-                        MidSlotPointers ++
-                        [{pointer, Self, RSlot, all, EndKey}];
-                false ->
-                    [{pointer, Self, LSlot, StartKey, all}] ++
-                        MidSlotPointers ++
-                        [{pointer, Self, RSlot, all, all}]
-            end
     end;
 fetch_range(_StartKey, _EndKey, _Summary, _FilterFun, false) ->
+    %% This has been pre-checked to be uninteresting (i.e. due to modified date)
     [].
 
 -spec compress_level(
@@ -2224,7 +2210,11 @@ read_slots(Handle, SlotList, {SegChecker, LowLastMod, BlockIndexCache},
                     % If there is an attempt to use the seg list query and the
                     % index block cache isn't cached for any part this may be
                     % slower as each slot will be read in turn
-                    {true, read_slotlist([Pointer], Handle) ++ Acc};
+                    {
+                        true,
+                        append(
+                            read_slotlist([Pointer], Handle), Acc)
+                        };
                 {BlockLengths, LMD, BlockIdx} ->
                     % If there is a BlockIndex cached then we can use it to
                     % check to see if any of the expected segments are
@@ -2242,10 +2232,14 @@ read_slots(Handle, SlotList, {SegChecker, LowLastMod, BlockIndexCache},
                             case SegChecker of
                                 false ->
                                     % No SegChecker - need all the slot now
-                                    {NeededBlockIdx,
+                                    {
-                                        read_slotlist([Pointer], Handle) ++ Acc
+                                        NeededBlockIdx,
+                                        append(
+                                            read_slotlist([Pointer], Handle),
+                                            Acc
+                                        )
                                     };
-                                SegChecker ->
+                                _ ->
                                     TrimmedKVL =
                                         checkblocks_segandrange(
                                             BlockIdx,
@@ -2255,7 +2249,7 @@ read_slots(Handle, SlotList, {SegChecker, LowLastMod, BlockIndexCache},
                                             IdxModDate,
                                             SegChecker,
                                             {SK, EK}),
-                                    {NeededBlockIdx, TrimmedKVL ++ Acc}
+                                    {NeededBlockIdx, append(TrimmedKVL, Acc)}
                             end
                     end
             end
@@ -2318,10 +2312,14 @@ binaryslot_reader(
     % of get_kvreader calls.  This means that slots which are only used in
     % range queries can still populate their block_index caches (on the FSM
     % loop state), and those caches can be used for future queries.
-    {Acc, BIAcc} =
     binaryslot_reader(
-            SlotBinsToFetch, PressMethod, IdxModDate, SegChecker, [], []),
+        lists:reverse(SlotBinsToFetch),
-    {lists:reverse(lists:reverse(SlotsToPoint) ++ Acc), BIAcc}.
+        PressMethod,
+        IdxModDate,
+        SegChecker,
+        SlotsToPoint,
+        []
+    ).
 
 binaryslot_reader([], _PressMethod, _IdxModDate, _SegChecker, Acc, BIAcc) ->
     {Acc, BIAcc};
@@ -2335,17 +2333,18 @@ binaryslot_reader(
     % entries in this slot to be trimmed from either or both sides.
     {TrimmedL, BICache} =
         binaryslot_trimmed(
-            SlotBin, SK, EK, PressMethod, IdxModDate, SegChecker),
+            SlotBin, SK, EK, PressMethod, IdxModDate, SegChecker, Acc
+        ),
     binaryslot_reader(
-        Tail, PressMethod, IdxModDate, SegChecker,
+        Tail,
-            lists:reverse(TrimmedL) ++ Acc, [{ID, BICache}|BIAcc]);
+        PressMethod,
-binaryslot_reader(L, PressMethod, IdxModDate, SegChecker, Acc, BIAcc) ->
+        IdxModDate,
-    {KVs, Tail} = lists:splitwith(fun(SR) -> tuple_size(SR) == 2 end, L),
+        SegChecker,
-    % These entries must already have been filtered for membership inside any
+        TrimmedL,
-    % range used in the query.
+        [{ID, BICache}|BIAcc]
-    binaryslot_reader(
+    );
-        Tail, PressMethod, IdxModDate, SegChecker,
+binaryslot_reader([{K, V}|Tail], PM, IMD, SC, Acc, BIAcc) ->
-            lists:reverse(KVs) ++ Acc, BIAcc).
+    binaryslot_reader(Tail, PM, IMD, SC, [{K, V}|Acc], BIAcc).
 
 
 read_length_list(Handle, LengthList) ->
@@ -2386,28 +2385,13 @@ binaryslot_get(FullBin, Key, Hash, PressMethod, IdxModDate) ->
                 none}
     end.
 
-
+-spec binaryslot_tolist(
--spec binaryslot_blockstolist(
-        list(non_neg_integer()),
         binary(),
         press_method(),
-        list(leveled_codec:ledger_kv())) -> list(leveled_codec:ledger_kv()).
+        boolean(),
-binaryslot_blockstolist([], _Bin, _PressMethod, Acc) ->
+        list(leveled_codec:ledger_kv()|expandable_pointer()))
-    Acc;
-binaryslot_blockstolist([0|RestLengths], RestBin, PressMethod, Acc) ->
-    binaryslot_blockstolist(RestLengths, RestBin, PressMethod, Acc);
-binaryslot_blockstolist([L|RestLengths], Bin, PressMethod, Acc) ->
-    <<Block:L/binary, RestBin/binary>> = Bin,
-    binaryslot_blockstolist(
-        RestLengths,
-        RestBin,
-        PressMethod,
-        Acc ++ deserialise_block(Block, PressMethod)).
-
--spec binaryslot_tolist(
-        binary(), press_method(), boolean())
             -> list(leveled_codec:ledger_kv()).
-binaryslot_tolist(FullBin, PressMethod, IdxModDate) ->
+binaryslot_tolist(FullBin, PressMethod, IdxModDate, InitAcc) ->
     case crc_check_slot(FullBin) of
         {Header, Blocks} ->
             {BlockLengths, _LMD, _PosBinIndex} =
@@ -2417,10 +2401,20 @@ binaryslot_tolist(FullBin, PressMethod, IdxModDate) ->
                 B3L:32/integer,
                 B4L:32/integer,
                 B5L:32/integer>> = BlockLengths,
-            binaryslot_blockstolist(
+            <<B1:B1L/binary,
-                [B1L, B2L, B3L, B4L, B5L], Blocks, PressMethod, []);
+                B2:B2L/binary,
+                B3:B3L/binary,
+                B4:B4L/binary,
+                B5:B5L/binary>> = Blocks,
+            lists:foldl(
+                fun(B, Acc) ->
+                    append(deserialise_block(B, PressMethod), Acc)
+                end,
+                InitAcc,
+                [B5, B4, B3, B2, B1]
+            );
         crc_wonky ->
-            []
+            InitAcc
     end.
 
 -spec binaryslot_trimmed(
@@ -2429,16 +2423,19 @@ binaryslot_tolist(FullBin, PressMethod, IdxModDate) ->
         range_endpoint(),
         press_method(),
         boolean(),
-        segment_check_fun()) ->
+        segment_check_fun(),
+        list(leveled_codec:ledger_kv()|expandable_pointer())
+    ) ->
             {list(leveled_codec:ledger_kv()),
                 list({integer(), binary()})|none}.
 %% @doc
 %% Must return a trimmed and reversed list of results in the range
 binaryslot_trimmed(
-        FullBin, all, all, PressMethod, IdxModDate, false) ->
+        FullBin, all, all, PressMethod, IdxModDate, false, Acc) ->
-    {binaryslot_tolist(FullBin, PressMethod, IdxModDate), none};
+    {binaryslot_tolist(FullBin, PressMethod, IdxModDate, Acc), none};
 binaryslot_trimmed(
-        FullBin, StartKey, EndKey, PressMethod, IdxModDate, SegmentChecker) ->
+        FullBin, StartKey, EndKey, PressMethod, IdxModDate, SegmentChecker, Acc
+    ) ->
     case {crc_check_slot(FullBin), SegmentChecker} of
         % Get a trimmed list of keys in the slot based on the range, trying
         % to minimise the number of blocks which are deserialised by
@@ -2459,7 +2456,7 @@ binaryslot_trimmed(
                     {StartKey, EndKey},
                     Block1, Block2, MidBlock, Block4, Block5,
                     PressMethod),
-            {TrimmedKVL, none};
+            {append(TrimmedKVL, Acc), none};
         {{Header, _Blocks}, SegmentChecker} ->
             {BlockLengths, _LMD, BlockIdx} =
                 extract_header(Header, IdxModDate),
@@ -2472,9 +2469,9 @@ binaryslot_trimmed(
                     IdxModDate,
                     SegmentChecker,
                     {StartKey, EndKey}),
-            {TrimmedKVL, Header};
+            {append(TrimmedKVL, Acc), Header};
         {crc_wonky, _} ->
-            {[], none}
+            {Acc, none}
     end.
 
 -spec blocks_required(
@@ -2487,27 +2484,35 @@ blocks_required(
     case filterby_midblock(
             fetchends_rawblock(MidBlockList), {StartKey, EndKey}) of
         empty ->
-            in_range(deserialise_block(B1, PressMethod), StartKey, EndKey)
+            append(
-            ++ in_range(deserialise_block(B2, PressMethod), StartKey, EndKey)
+                in_range(deserialise_block(B1, PressMethod), StartKey, EndKey),
-            ++ in_range(deserialise_block(B4, PressMethod), StartKey, EndKey)
+                in_range(deserialise_block(B2, PressMethod), StartKey, EndKey),
-            ++ in_range(deserialise_block(B5, PressMethod), StartKey, EndKey);
+                in_range(deserialise_block(B4, PressMethod), StartKey, EndKey),
+                in_range(deserialise_block(B5, PressMethod), StartKey, EndKey)
+            );
         all_blocks ->
-            get_lefthand_blocks(B1, B2, PressMethod, StartKey)
+            append(
-            ++ MidBlockList
+                get_lefthand_blocks(B1, B2, PressMethod, StartKey),
-            ++ get_righthand_blocks(B4, B5, PressMethod, EndKey);
+                MidBlockList,
+                get_righthand_blocks(B4, B5, PressMethod, EndKey)
+            );
         lt_mid ->
             in_range(
                 get_lefthand_blocks(B1, B2, PressMethod, StartKey),
                 all,
                 EndKey);
         le_mid ->
-            get_lefthand_blocks(B1, B2, PressMethod, StartKey)
+            append(
-            ++ in_range(MidBlockList, all, EndKey);
+                get_lefthand_blocks(B1, B2, PressMethod, StartKey),
+                in_range(MidBlockList, all, EndKey)
+            );
         mid_only ->
             in_range(MidBlockList, StartKey, EndKey);
         ge_mid ->
-            in_range(MidBlockList, StartKey, all)
+            append(
-            ++ get_righthand_blocks(B4, B5, PressMethod, EndKey);
+                in_range(MidBlockList, StartKey, all),
+                get_righthand_blocks(B4, B5, PressMethod, EndKey)
+            );
         gt_mid ->
             in_range(
                 get_righthand_blocks(B4, B5, PressMethod, EndKey),
@@ -2695,6 +2700,34 @@ revert_position(Pos) ->
             end
     end.
 
+%%%============================================================================
+%%% Optimised list functions
+%%%============================================================================
+
+
+%% @doc See eunit test append_performance_test_/0 and also
+%% https://github.com/erlang/otp/pull/8743
+%% On OTP 26.2.1 -
+%% Time for plus plus 16565
+%% Time for append 7453
+%% Time for lists:append 16428
+%% Time for right associative plus plus 15928
+%% ... this is all about optimising the case where there is an empty list
+%% on the RHS ... and the absolute benefit is marginal
+-spec append(list(), list()) -> list().
+append(L1, []) ->
+    L1;
+append(L1, L2) ->
+    L1 ++ L2.
+
+-spec append(list(), list(), list()) -> list().
+append(L1, L2, L3) ->
+    append(L1, append(L2, L3)).
+
+-spec append(list(), list(), list(), list()) -> list().
+append(L1, L2, L3, L4) ->
+    append(L1, append(L2, L3, L4)).
+
 %%%============================================================================
 %%% Merge Functions
 %%%============================================================================
@@ -3060,6 +3093,15 @@ maybelog_fetch_timing({Pid, _SlotFreq}, Level, Type, SW) ->
 
 -define(TEST_AREA, "test/test_area/").
 
+binaryslot_trimmed(
+    FullBin, StartKey, EndKey, PressMethod, IdxModDate, SegmentChecker) ->
+    binaryslot_trimmed(
+        FullBin, StartKey, EndKey, PressMethod, IdxModDate, SegmentChecker, []
+    ).
+
+binaryslot_tolist(FullBin, PressMethod, IdxModDate) ->
+    binaryslot_tolist(FullBin, PressMethod, IdxModDate, []).
+
 
 sst_getkvrange(Pid, StartKey, EndKey, ScanWidth) ->
     sst_getkvrange(Pid, StartKey, EndKey, ScanWidth, false, 0).
@@ -3146,11 +3188,60 @@ generate_indexkeys(Count, IndexList) ->
 
 generate_indexkey(Term, Count) ->
     IndexSpecs = [{add, "t1_int", Term}],
-    leveled_codec:idx_indexspecs(IndexSpecs,
+    leveled_codec:idx_indexspecs(
+        IndexSpecs,
         "Bucket",
         "Key" ++ integer_to_list(Count),
         Count,
-                                    infinity).
+        infinity
+    ).
+
+append_performance_test_() ->
+    {timeout, 300, fun append_performance_tester/0}.
+
+append_performance_tester() ->
+    KVL1 = generate_randomkeys(0, 128, 1, 4),
+    KVL2 = generate_randomkeys(129, 256, 1, 4),
+    KVL3 = generate_randomkeys(257, 384, 1, 4),
+    KVL4 = generate_randomkeys(385, 512, 1, 4),
+
+    SW0 = os:system_time(microsecond),
+    lists:foreach(
+        fun(_I) ->
+            _KVL = KVL1 ++ KVL2 ++ KVL3 ++ KVL4 ++ []
+        end,
+        lists:seq(1, 5000)
+    ),
+    SW1 = os:system_time(microsecond),
+    lists:foreach(
+        fun(_I) ->
+            _KVL = append(KVL1, KVL2, KVL3, append(KVL4, []))
+        end,
+        lists:seq(1, 5000)
+    ),
+    SW2 = os:system_time(microsecond),
+    lists:foreach(
+        fun(_I) ->
+            _KVL = lists:append([KVL1, KVL2, KVL3, KVL4, []])
+        end,
+        lists:seq(1, 5000)
+    ),
+    SW3 = os:system_time(microsecond),
+    lists:foreach(
+        fun(_I) ->
+            _KVL = KVL1 ++ (KVL2 ++ (KVL3 ++ (KVL4 ++ [])))
+        end,
+        lists:seq(1, 5000)
+    ),
+    SW4 = os:system_time(microsecond),
+    io:format(
+        user,
+        "~nTime for plus plus ~w "
+        "Time for inline append ~w "
+        "Time for lists:append ~w "
+        "Time for bidmas plus plus ~w~n",
+        [SW1 - SW0, SW2 - SW1, SW3 - SW2, SW4 - SW3]
+    ).
 
 tombcount_test() ->
     tombcount_tester(1),
@@ -3957,6 +4048,9 @@ fetch_status_test() ->
     ST = maps:get(state, Status),
     ?assertMatch(redacted, ST#state.blockindex_cache),
     ?assertMatch(redacted, ST#state.fetch_cache),
+    NormStatus = format_status(#{reason => normal, state => S}),
+    NST = maps:get(state, NormStatus),
+    ?assert(is_integer(array:size(NST#state.fetch_cache))),
     ok = sst_close(Pid),
     ok = file:delete(filename:join(RP, Filename ++ ".sst")).
 

src/leveled_tictac.erl

@@ -418,9 +418,9 @@ generate_segmentfilter_list(SegmentList, xsmall) ->
             A1 = 1 bsl 14,
             ExpandSegFun = 
                 fun(X, Acc) -> 
-                    Acc ++ [X, X + A0, X + A1, X + A0 + A1]
+                    [X, X + A0, X + A1, X + A0 + A1] ++ Acc
                 end,
-            lists:foldl(ExpandSegFun, [], SegmentList);
+            lists:foldr(ExpandSegFun, [], SegmentList);
         false ->
             false
     end;

src/leveled_util.erl

@@ -5,12 +5,15 @@
 
 -module(leveled_util).
 
--export([generate_uuid/0,
+-export([
+            generate_uuid/0,
             integer_now/0,
             integer_time/1,
             magic_hash/1,
             t2b/1,
-            safe_rename/4]).
+            safe_rename/4
+        ]
+    ).
 
 -define(WRITE_OPS, [binary, raw, read, write]).