Make the top_level parameter configurable.

README.md

@@ -82,7 +82,13 @@ Put these values in your `app.config` in the `hanoidb` section
           %% Both have same log2(N) worst case, but `fast' is
           %% sometimes faster; yielding latency fluctuations.
           %%
-          {merge_strategy, fast | predictable}
+          {merge_strategy, fast | predictable},
+
+          %% "Level0" files has 2^N KVs in it, defaulting to 1024.
+          %% If the database is to contain very small KVs, this is
+          %% likely too small, and will result in many unnecessary
+          %% file operations.  (Subsequent levels double in size).
+          {top_level, 10}  % 1024 Key/Values
          ]},
 ```
 

src/hanoidb.erl

@@ -70,6 +70,7 @@
                        | {sync_strategy, none | sync | {seconds, pos_integer()}}
                        | {expiry_secs, non_neg_integer()}
                        | {spawn_opt, list()}
+                       | {top_level, pos_integer()}
                        .
 
 %% @doc
@@ -278,24 +279,26 @@ init([Dir, Opts0]) ->
         end,
     hanoidb_util:ensure_expiry(Opts),
 
-    {Nursery, MaxLevel, TopLevel} =
+    {Top, Nur, Max} =
         case file:read_file_info(Dir) of
             {ok, #file_info{ type=directory }} ->
-                {ok, TL, ML} = open_levels(Dir, Opts),
+                {ok, TopLevel, MinLevel, MaxLevel} = open_levels(Dir, Opts),
-                {ok, N0} = hanoidb_nursery:recover(Dir, TL, ML, Opts),
+                {ok, Nursery} = hanoidb_nursery:recover(Dir, TopLevel, MinLevel, MaxLevel, Opts),
-                {N0, ML, TL};
+                {TopLevel, Nursery, MaxLevel};
             {error, E} when E =:= enoent ->
                 ok = file:make_dir(Dir),
-                {ok, TL} = hanoidb_level:open(Dir, ?TOP_LEVEL, undefined, Opts, self()),
+                MinLevel = get_opt(top_level, Opts0, ?TOP_LEVEL),
-                ML = ?TOP_LEVEL,
+                {ok, TopLevel} = hanoidb_level:open(Dir, MinLevel, undefined, Opts, self()),
-                {ok, N0} = hanoidb_nursery:new(Dir, ML, Opts),
+                MaxLevel = MinLevel,
-                {N0, ML, TL}
+                {ok, Nursery} = hanoidb_nursery:new(Dir, MinLevel, MaxLevel, Opts),
-            end,
+                {TopLevel, Nursery, MaxLevel}
-    {ok, #state{ top=TopLevel, dir=Dir, nursery=Nursery, opt=Opts, max_level=MaxLevel }}.
+        end,
+    {ok, #state{ top=Top, dir=Dir, nursery=Nur, opt=Opts, max_level=Max }}.
 
 
 open_levels(Dir, Options) ->
     {ok, Files} = file:list_dir(Dir),
+    TopLevel0 = get_opt(top_level, Options, ?TOP_LEVEL),
 
     %% parse file names and find max level
     {MinLevel, MaxLevel} =
@@ -308,7 +311,7 @@ open_levels(Dir, Options) ->
                                     {MinLevel, MaxLevel}
                             end
                     end,
-                    {?TOP_LEVEL, ?TOP_LEVEL},
+                    {TopLevel0, TopLevel0},
                     Files),
 
     %% remove old nursery data file
@@ -323,17 +326,17 @@ open_levels(Dir, Options) ->
                             {Level, MergeWork}
                     end,
                     {undefined, 0},
-                    lists:seq(MaxLevel, min(?TOP_LEVEL, MinLevel), -1)),
+                    lists:seq(MaxLevel, MinLevel, -1)),
-    WorkPerIter = (MaxLevel - MinLevel + 1) * ?BTREE_SIZE(?TOP_LEVEL),
+    WorkPerIter = (MaxLevel - MinLevel + 1) * ?BTREE_SIZE(MinLevel),
 %    error_logger:info_msg("do_merge ... {~p,~p,~p}~n", [TopLevel, WorkPerIter, MaxMerge]),
-    do_merge(TopLevel, WorkPerIter, MaxMerge),
+    do_merge(TopLevel, WorkPerIter, MaxMerge, MinLevel),
-    {ok, TopLevel, MaxLevel}.
+    {ok, TopLevel, MinLevel, MaxLevel}.
 
-do_merge(TopLevel, _Inc, N) when N =< 0 ->
+do_merge(TopLevel, _Inc, N, _MinLevel) when N =< 0 ->
     ok = hanoidb_level:await_incremental_merge(TopLevel);
-do_merge(TopLevel, Inc, N) ->
+do_merge(TopLevel, Inc, N, MinLevel) ->
-    ok = hanoidb_level:begin_incremental_merge(TopLevel, ?BTREE_SIZE(?TOP_LEVEL)),
+    ok = hanoidb_level:begin_incremental_merge(TopLevel, ?BTREE_SIZE(MinLevel)),
-    do_merge(TopLevel, Inc, N-Inc).
+    do_merge(TopLevel, Inc, N-Inc, MinLevel).
 
 
 parse_level(FileName) ->
@@ -413,7 +416,8 @@ handle_call(close, _From, State=#state{ nursery=undefined }) ->
 handle_call(close, _From, State=#state{ nursery=Nursery, top=Top, dir=Dir, max_level=MaxLevel, opt=Config }) ->
     try
         ok = hanoidb_nursery:finish(Nursery, Top),
-        {ok, Nursery2} = hanoidb_nursery:new(Dir, MaxLevel, Config),
+        MinLevel = hanoidb_level:level(Top),
+        {ok, Nursery2} = hanoidb_nursery:new(Dir, MinLevel, MaxLevel, Config),
         ok = hanoidb_level:close(Top),
         {stop, normal, ok, State#state{ nursery=Nursery2 }}
     catch
@@ -423,9 +427,10 @@ handle_call(close, _From, State=#state{ nursery=Nursery, top=Top, dir=Dir, max_l
     end;
 
 handle_call(destroy, _From, State=#state{top=Top, nursery=Nursery }) ->
+    TopLevelNumber = hanoidb_level:level(Top),
     ok = hanoidb_nursery:destroy(Nursery),
     ok = hanoidb_level:destroy(Top),
-    {stop, normal, ok, State#state{ top=undefined, nursery=undefined, max_level=?TOP_LEVEL }}.
+    {stop, normal, ok, State#state{ top=undefined, nursery=undefined, max_level=TopLevelNumber }}.
 
 -spec do_put(key(), value(), expiry(), #state{}) -> {ok, #state{}}.
 do_put(Key, Value, Expiry, State=#state{ nursery=Nursery, top=Top }) when Nursery =/= undefined ->

src/hanoidb.hrl

@@ -23,8 +23,8 @@
 %% ----------------------------------------------------------------------------
 
 
-%% smallest levels are 256 entries
+%% smallest levels are 1024 entries
--define(TOP_LEVEL, 8).
+-define(TOP_LEVEL, 10).
 -define(BTREE_SIZE(Level), (1 bsl (Level))).
 -define(FILE_FORMAT, <<"HAN2">>).
 -define(FIRST_BLOCK_POS, byte_size(?FILE_FORMAT)).
@@ -54,6 +54,7 @@
                    total_size=0 :: integer(),
                    count=0 :: integer(),
                    last_sync=now() :: erlang:timestamp(),
+                   min_level :: integer(),
                    max_level :: integer(),
                    config=[] :: [{atom(), term()}],
                    step=0 :: integer(),

src/hanoidb_level.erl

@@ -46,7 +46,7 @@
 
 -export([open/5, lookup/2, lookup/3, inject/2, close/1, snapshot_range/3, blocking_range/3,
          begin_incremental_merge/2, await_incremental_merge/1, set_max_level/2,
-         unmerged_count/1, destroy/1]).
+         unmerged_count/1, destroy/1, level/1]).
 
 -include_lib("kernel/include/file.hrl").
 
@@ -90,6 +90,9 @@ open(Dir,Level,Next,Opts,Owner) when Level>0 ->
                               SpawnOpt),
     {ok, PID}.
 
+level(Ref) ->
+    plain_rpc:call(Ref, level).
+
 lookup(Ref, Key) ->
     plain_rpc:call(Ref, {lookup, Key}).
 
@@ -356,6 +359,11 @@ main_loop(State = #state{ next=Next }) ->
                ->
             do_step(StepFrom, DoneWork, StepSize, State);
 
+        %% simply replies the level number
+        ?CALL(From, level) ->
+            plain_rpc:send_reply(From, State#state.level),
+            main_loop(State);
+
         {MRef, step_done} when MRef == State#state.step_merge_ref ->
             demonitor(MRef, [flush]),
 

src/hanoidb_nursery.erl

@@ -25,40 +25,39 @@
 -module(hanoidb_nursery).
 -author('Kresten Krab Thorup <krab@trifork.com>').
 
--export([new/3, recover/4, finish/2, lookup/2, add/4, add/5]).
+-export([new/4, recover/5, finish/2, lookup/2, add/4, add/5]).
 -export([do_level_fold/3, set_max_level/2, transact/3, destroy/1]).
 
 -include("include/hanoidb.hrl").
 -include("hanoidb.hrl").
 -include_lib("kernel/include/file.hrl").
 
--spec new(string(), integer(), [_]) -> {ok, #nursery{}} | {error, term()}.
+-spec new(string(), integer(), integer(), [_]) -> {ok, #nursery{}} | {error, term()}.
 
 -define(LOGFILENAME(Dir), filename:join(Dir, "nursery.log")).
 
 %% do incremental merge every this many inserts
 %% this value *must* be less than or equal to
 %% 2^TOP_LEVEL == ?BTREE_SIZE(?TOP_LEVEL)
--define(INC_MERGE_STEP, ?BTREE_SIZE(?TOP_LEVEL)/2).
+-define(INC_MERGE_STEP, ?BTREE_SIZE(MinLevel) div 2).
 
-new(Directory, MaxLevel, Config) ->
+new(Directory, MinLevel, MaxLevel, Config) ->
     hanoidb_util:ensure_expiry(Config),
 
     {ok, File} = file:open(?LOGFILENAME(Directory),
                             [raw, exclusive, write, delayed_write, append]),
     {ok, #nursery{ log_file=File, dir=Directory, cache= gb_trees:empty(),
-                   max_level=MaxLevel, config=Config }}.
+                   min_level=MinLevel, max_level=MaxLevel, config=Config }}.
 
 
-recover(Directory, TopLevel, MaxLevel, Config) ->
+recover(Directory, TopLevel, MinLevel, MaxLevel, Config) ->
     hanoidb_util:ensure_expiry(Config),
-
     case file:read_file_info(?LOGFILENAME(Directory)) of
         {ok, _} ->
             ok = do_recover(Directory, TopLevel, MaxLevel, Config),
-            new(Directory, MaxLevel, Config);
+            new(Directory, MinLevel, MaxLevel, Config);
         {error, enoent} ->
-            new(Directory, MaxLevel, Config)
+            new(Directory, MinLevel, MaxLevel, Config)
     end.
 
 do_recover(Directory, TopLevel, MaxLevel, Config) ->
@@ -175,7 +174,7 @@ lookup(Key, #nursery{cache=Cache}) ->
 %% @end
 -spec finish(Nursery::#nursery{}, TopLevel::pid()) -> ok.
 finish(#nursery{ dir=Dir, cache=Cache, log_file=LogFile, merge_done=DoneMerge,
-                 count=Count, config=Config }, TopLevel) ->
+                 count=Count, config=Config, min_level=MinLevel }, TopLevel) ->
 
     hanoidb_util:ensure_expiry(Config),
 
@@ -189,7 +188,7 @@ finish(#nursery{ dir=Dir, cache=Cache, log_file=LogFile, merge_done=DoneMerge,
         N when N > 0 ->
             %% next, flush cache to a new BTree
             BTreeFileName = filename:join(Dir, "nursery.data"),
-            {ok, BT} = hanoidb_writer:open(BTreeFileName, [{size, ?BTREE_SIZE(?TOP_LEVEL)},
+            {ok, BT} = hanoidb_writer:open(BTreeFileName, [{size, ?BTREE_SIZE(MinLevel)},
                                                            {compress, none} | Config]),
             try
                 ok = gb_trees_ext:fold(fun(Key, Value, Acc) ->
@@ -205,10 +204,10 @@ finish(#nursery{ dir=Dir, cache=Cache, log_file=LogFile, merge_done=DoneMerge,
 
             %% Issue some work if this is a top-level inject (blocks until previous such
             %% incremental merge is finished).
-            if DoneMerge >= ?BTREE_SIZE(?TOP_LEVEL) ->
+            if DoneMerge >= ?BTREE_SIZE(MinLevel) ->
                     ok;
                true ->
-                    hanoidb_level:begin_incremental_merge(TopLevel, ?BTREE_SIZE(?TOP_LEVEL) - DoneMerge)
+                    hanoidb_level:begin_incremental_merge(TopLevel, ?BTREE_SIZE(MinLevel) - DoneMerge)
             end;
 %            {ok, _Nursery2} = do_inc_merge(Nursery, Count, TopLevel);
 
@@ -247,13 +246,13 @@ add(Key, Value, Expiry, Nursery, Top) ->
     end.
 
 -spec flush(#nursery{}, pid()) -> {ok, #nursery{}}.
-flush(Nursery=#nursery{ dir=Dir, max_level=MaxLevel, config=Config }, Top) ->
+flush(Nursery=#nursery{ dir=Dir, min_level=MinLevel, max_level=MaxLevel, config=Config }, Top) ->
     ok = finish(Nursery, Top),
     {error, enoent} = file:read_file_info(filename:join(Dir, "nursery.log")),
-    hanoidb_nursery:new(Dir, MaxLevel, Config).
+    hanoidb_nursery:new(Dir, MinLevel,  MaxLevel, Config).
 
-has_room(#nursery{ count=Count }, N) ->
+has_room(#nursery{ count=Count, min_level=MinLevel }, N) ->
-    (Count + N + 1) < ?BTREE_SIZE(?TOP_LEVEL).
+    (Count + N + 1) < ?BTREE_SIZE(MinLevel).
 
 ensure_space(Nursery, NeededRoom, Top) ->
     case has_room(Nursery, NeededRoom) of
@@ -303,7 +302,7 @@ transact1(Spec, Nursery1=#nursery{ log_file=File, cache=Cache0, total_size=Total
 
     do_inc_merge(Nursery2#nursery{ cache=Cache2, total_size=TotalSize+erlang:iolist_size(Data), count=Count }, length(Spec), Top).
 
-do_inc_merge(Nursery=#nursery{ step=Step, merge_done=Done }, N, TopLevel) ->
+do_inc_merge(Nursery=#nursery{ step=Step, merge_done=Done, min_level=MinLevel }, N, TopLevel) ->
     if Step+N >= ?INC_MERGE_STEP ->
             hanoidb_level:begin_incremental_merge(TopLevel, Step + N),
             {ok, Nursery#nursery{ step=0, merge_done=Done + Step + N }};