Use backend API in nursery also

First step towards a hanoidb backend API, which
will allow replacing the storage engine with
any ordered storage.

We still need an API for how to choose backend
and perhaps also how to discover the backend
of an existing store.

include/plain_rpc.hrl

@@ -27,3 +27,5 @@
 -define(REPLY(Ref,Msg), {'$reply', Ref, Msg}).
 -define(CAST(From,Msg), {'$cast', From, Msg}).
 
+-type caller() :: { pid(), reference() }.
+

src/hanoidb.hrl

@@ -57,7 +57,9 @@
                    max_level :: integer(),
                    config=[] :: [{atom(), term()}],
                    step=0 :: integer(),
-                   merge_done=0 :: integer()}).
+                   merge_done=0 :: integer(),
+                   backend = hanoidb_han2_backend :: atom()
+                 }).
 
 -type kventry() :: { key(), expvalue() } | [ kventry() ].
 -type key() :: binary().

src/hanoidb_backend.erl

@@ -0,0 +1,174 @@
+
+-module(hanoidb_backend).
+
+-include("include/hanoidb.hrl").
+-include("src/hanoidb.hrl").
+
+-type options() :: [ atom() | { atom(), term() } ].
+-type kvexp_entry() :: { Key :: key(), Value :: value(), TimeOut :: expiry() }.
+-type batch_reader() :: any().
+-type batch_writer() :: any().
+-type random_reader() :: any().
+
+-export([merge/7]).
+
+%%%=========================================================================
+%%%  API
+%%%=========================================================================
+
+%% batch_reader and batch_writer are used by the merging logic.  A batch_reader
+%% must return the values in lexicographical order of the binary keys.
+
+-callback open_batch_reader(File :: string(), Options :: options())
+    -> {ok, batch_reader()} | { error, term() }.
+-callback read_next(batch_reader())
+    -> { [kvexp_entry(), ...], batch_reader()} | 'done'.
+-callback close_batch_reader( batch_reader() )
+    -> ok | {error, term()}.
+
+
+-callback open_batch_writer(File :: string(), Options :: options())
+    -> {ok, batch_writer()} | {error, term()}.
+-callback write_next( kvexp_entry() , batch_writer() )
+    -> {ok, batch_writer()} | {error, term()}.
+-callback write_count( batch_writer() ) ->
+    {ok, non_neg_integer()} | {error, term()}.
+-callback close_batch_writer( batch_writer() )
+    -> ok | {error, term()}.
+
+
+-callback open_random_reader(File :: string(), Options :: options()) ->
+    {ok, random_reader()} | {error, term()}.
+-callback file_name( random_reader() ) ->
+    {ok, string()} | {error, term()}.
+-callback lookup( Key :: key(), random_reader() ) ->
+    not_found | {ok, value()}.
+-callback range_fold( fun( (key(), value(), term()) -> term() ),
+                      Acc0   :: term(),
+                      Reader :: random_reader(),
+                      Range  :: #key_range{} ) ->
+    {limit, term(), LastKey :: binary()} | {ok, term()}.
+-callback close_random_reader(random_reader()) ->
+    ok | {error, term()}.
+
+
+
+
+-spec merge(atom(), string(), string(), string(), integer(), boolean(), list()) -> {ok, integer()}.
+merge(Mod,A,B,C, Size, IsLastLevel, Options) ->
+    {ok, IXA} = Mod:open_batch_reader(A, Options),
+    {ok, IXB} = Mod:open_batch_reader(B, Options),
+    {ok, Out} = Mod:open_batch_writer(C, [{size, Size} | Options]),
+    scan(Mod,IXA, IXB, Out, IsLastLevel, [], [], {0, none}).
+
+terminate(Mod, Out) ->
+    {ok, Count} = Mod:write_count( Out ),
+    ok = Mod:close_batch_writer( Out ),
+    {ok, Count}.
+
+step(S) ->
+    step(S, 1).
+
+step({N, From}, Steps) ->
+    {N-Steps, From}.
+
+
+scan(Mod, IXA, IXB, Out, IsLastLevel, AKVs, BKVs, {N, FromPID}) when N < 1, AKVs =/= [], BKVs =/= [] ->
+    case FromPID of
+        none ->
+            ok;
+        {PID, Ref} ->
+            PID ! {Ref, step_done}
+    end,
+
+    receive
+        {step, From, HowMany} ->
+            scan(Mod, IXA, IXB, Out, IsLastLevel, AKVs, BKVs, {N+HowMany, From})
+    end;
+
+scan(Mod, IXA, IXB, Out, IsLastLevel, [], BKVs, Step) ->
+    case Mod:read_next(IXA) of
+        {AKVs, IXA2} ->
+            scan(Mod, IXA2, IXB, Out, IsLastLevel, AKVs, BKVs, Step);
+        done ->
+            ok = Mod:close_batch_reader(IXA),
+            scan_only(Mod, IXB, Out, IsLastLevel, BKVs, Step)
+    end;
+
+scan(Mod, IXA, IXB, Out, IsLastLevel, AKVs, [], Step) ->
+    case Mod:read_next(IXB) of
+        {BKVs, IXB2} ->
+            scan(Mod, IXA, IXB2, Out, IsLastLevel, AKVs, BKVs, Step);
+        done ->
+            ok = Mod:close_batch_reader(IXB),
+            scan_only(Mod, IXA, Out, IsLastLevel, AKVs, Step)
+    end;
+
+scan(Mod, IXA, IXB, Out, IsLastLevel, [{Key1,_,_}=Entry|AT], [{Key2,_,_}|_]=BKVs, Step)
+  when Key1 < Key2 ->
+    case Entry of
+        {_, ?TOMBSTONE, _} when IsLastLevel ->
+            scan(Mod, IXA, IXB, Out, true, AT, BKVs, step(Step));
+        _ ->
+            {ok, Out3} = Mod:write_next( Entry, Out ),
+            scan(Mod, IXA, IXB, Out3, IsLastLevel, AT, BKVs, step(Step))
+    end;
+scan(Mod, IXA, IXB, Out, IsLastLevel, [{Key1,_,_}|_]=AKVs, [{Key2,_,_}=Entry|BT], Step)
+  when Key1 > Key2 ->
+    case Entry of
+        {_, ?TOMBSTONE, _} when IsLastLevel ->
+            scan(Mod, IXA, IXB, Out, true, AKVs, BT, step(Step));
+        _ ->
+            {ok, Out3} = Mod:write_next( Entry, Out ),
+            scan(Mod, IXA, IXB, Out3, IsLastLevel, AKVs, BT, step(Step))
+    end;
+scan(Mod, IXA, IXB, Out, IsLastLevel, [_|AT], [Entry|BT], Step) ->
+    case Entry of
+        {_, ?TOMBSTONE, _} when IsLastLevel ->
+            scan(Mod, IXA, IXB, Out, true, AT, BT, step(Step));
+        _ ->
+            {ok, Out3} = Mod:write_next( Entry, Out ),
+            scan(Mod, IXA, IXB, Out3, IsLastLevel, AT, BT, step(Step, 2))
+    end.
+
+
+scan_only(Mod, IX, Out, IsLastLevel, KVs, {N, FromPID}) when N < 1, KVs =/= [] ->
+    case FromPID of
+        none ->
+            ok;
+        {PID, Ref} ->
+            PID ! {Ref, step_done}
+    end,
+
+    receive
+        {step, From, HowMany} ->
+            scan_only(Mod, IX, Out, IsLastLevel, KVs, {N+HowMany, From})
+    end;
+
+scan_only(Mod, IX, Out, IsLastLevel, [], {_, FromPID}=Step) ->
+    case Mod:read_next(IX) of
+        {KVs, IX2} ->
+            scan_only(Mod, IX2, Out, IsLastLevel, KVs, Step);
+        done ->
+            case FromPID of
+                none ->
+                    ok;
+                {PID, Ref} ->
+                    PID ! {Ref, step_done}
+            end,
+            ok = Mod:close_batch_reader(IX),
+            terminate(Mod, Out)
+    end;
+
+scan_only(Mod, IX, Out, true, [{_,?TOMBSTONE,_}|Rest], Step) ->
+    scan_only(Mod, IX, Out, true, Rest, step(Step));
+
+scan_only(Mod, IX, Out, IsLastLevel, [Entry|Rest], Step) ->
+    {ok, Out3} = Mod:write_next( Entry, Out ),
+    scan_only(Mod, IX, Out3, IsLastLevel, Rest, step(Step)).
+
+
+
+
+
+

src/hanoidb_han2_backend.erl

@@ -0,0 +1,70 @@
+-module(hanoidb_han2_backend).
+
+-include("hanoidb.hrl").
+
+-behavior(hanoidb_backend).
+
+-export([open_random_reader/2, file_name/1, range_fold/4, lookup/2, close_random_reader/1]).
+-export([open_batch_reader/2, read_next/1, close_batch_reader/1]).
+-export([open_batch_writer/2, write_next/2, write_count/1, close_batch_writer/1]).
+
+
+open_random_reader(Name, Options) ->
+    hanoidb_reader:open(Name, [random|Options]).
+
+file_name(Reader) ->
+    hanoidb_reader:file_name(Reader).
+
+lookup(Key, Reader) ->
+    hanoidb_reader:lookup(Reader, Key).
+
+range_fold(Fun, Acc, Reader, Range) ->
+    hanoidb_reader:range_fold(Fun, Acc, Reader, Range).
+
+close_random_reader(Reader) ->
+    hanoidb_reader:close(Reader).
+
+
+
+open_batch_reader(Name, Options) ->
+    hanoidb_reader:open(Name, [sequential|Options]).
+
+read_next(Reader) ->
+    case hanoidb_reader:next_node(Reader) of
+        {node, KVs} ->
+            {[ unfold(KV) || KV <- KVs], Reader};
+        end_of_data ->
+            'done';
+        {error, _}=Err ->
+            Err
+    end.
+
+unfold({Key,{Value, Expiry}}) when is_binary(Value); ?TOMBSTONE =:= Value ->
+    {Key,Value,Expiry};
+unfold({Key,Value}) ->
+    {Key, Value, infinity}.
+
+close_batch_reader(Reader) ->
+    hanoidb_reader:close(Reader).
+
+open_batch_writer(Name, Options) ->
+    hanoidb_writer:init([Name, Options]).
+
+write_next( {Key, Value, infinity}, Writer) ->
+    {noreply, Writer2} = hanoidb_writer:handle_cast({add, Key, Value}, Writer),
+    {ok, Writer2};
+write_next( {Key, Value, Expiry}, Writer) ->
+    {noreply, Writer2} = hanoidb_writer:handle_cast({add, Key, {Value, Expiry}}, Writer),
+    {ok, Writer2}.
+
+write_count( Writer ) ->
+    case hanoidb_writer:handle_call(count, self(), Writer) of
+        {ok, Count, _} ->
+            {ok, Count};
+        Err ->
+            {error, Err}
+    end.
+
+close_batch_writer(Writer) ->
+    {stop, normal, ok, _} = hanoidb_writer:handle_call(close, self(), Writer),
+    ok.

src/hanoidb_level.erl

@@ -51,9 +51,24 @@
 -include_lib("kernel/include/file.hrl").
 
 -record(state, {
-          a, b, c, next, dir, level, inject_done_ref, merge_pid, folding = [],
-          step_next_ref, step_caller, step_merge_ref,
-          opts = [], owner, work_in_progress=0, work_done=0, max_level=?TOP_LEVEL
+          a :: undefined | hanoidb_backend:random_reader(),
+          b :: undefined | hanoidb_backend:random_reader(),
+          c :: undefined | hanoidb_backend:random_reader(),
+          next :: pid() | undefined,
+          dir :: string(),
+          level :: non_neg_integer(),
+          inject_done_ref :: reference(),
+          merge_pid :: pid(),
+          folding = [] :: list( pid() ),
+          step_next_ref :: reference() | undefined,
+          step_caller :: plain_rpc:caller() | undefined,
+          step_merge_ref :: reference() | undefined,
+          opts = [] :: list(),
+          owner :: pid(),
+          work_in_progress=0 :: non_neg_integer(),
+          work_done=0 :: non_neg_integer(),
+          max_level=?TOP_LEVEL :: pos_integer(),
+          backend = hanoidb_han2_backend :: atom()
           }).
 
 
@@ -177,6 +192,8 @@ initialize2(State) ->
     file:delete(filename("BF",State)),
     file:delete(filename("CF",State)),
 
+    Mod = State#state.backend,
+
     case file:read_file_info(MFileName) of
         {ok, _} ->
 
@@ -188,12 +205,12 @@ initialize2(State) ->
             file:delete(BFileName),
             ok = file:rename(MFileName, AFileName),
 
-            {ok, IXA} = hanoidb_reader:open(AFileName, [random|State#state.opts]),
+            {ok, IXA} = Mod:open_random_reader(AFileName, [random|State#state.opts]),
 
             case file:read_file_info(CFileName) of
                 {ok, _} ->
                     file:rename(CFileName, BFileName),
-                    {ok, IXB} = hanoidb_reader:open(BFileName, [random|State#state.opts]),
+                    {ok, IXB} = Mod:open_random_reader(BFileName, [random|State#state.opts]),
                     check_begin_merge_then_loop0(init_state(State#state{ a= IXA, b=IXB }));
 
                 {error, enoent} ->
@@ -203,13 +220,13 @@ initialize2(State) ->
         {error, enoent} ->
             case file:read_file_info(BFileName) of
                 {ok, _} ->
-                    {ok, IXA} = hanoidb_reader:open(AFileName, [random|State#state.opts]),
-                    {ok, IXB} = hanoidb_reader:open(BFileName, [random|State#state.opts]),
+                    {ok, IXA} = Mod:open_random_reader(AFileName, [random|State#state.opts]),
+                    {ok, IXB} = Mod:open_random_reader(BFileName, [random|State#state.opts]),
 
                     IXC =
                         case file:read_file_info(CFileName) of
                             {ok, _} ->
-                                {ok, C} = hanoidb_reader:open(CFileName, [random|State#state.opts]),
+                                {ok, C} = Mod:open_random_reader(CFileName, [random|State#state.opts]),
                                 C;
                         {error, enoent} ->
                             undefined
@@ -224,7 +241,7 @@ initialize2(State) ->
 
                     case file:read_file_info(AFileName) of
                         {ok, _} ->
-                            {ok, IXA} = hanoidb_reader:open(AFileName, [random|State#state.opts]),
+                            {ok, IXA} = Mod:open_random_reader(AFileName, [random|State#state.opts]),
                             main_loop(init_state(State#state{ a=IXA }));
 
                         {error, enoent} ->
@@ -263,28 +280,28 @@ check_begin_merge_then_loop(State=#state{a=IXA, b=IXB, merge_pid=undefined})
 check_begin_merge_then_loop(State) ->
     main_loop(State).
 
-main_loop(State = #state{ next=Next }) ->
+main_loop(State = #state{ next=Next, backend=Mod }) ->
     Parent = plain_fsm:info(parent),
     receive
         ?CALL(From, {lookup, Key})=Req ->
-            case do_lookup(Key, [State#state.c, State#state.b, State#state.a, Next]) of
-                not_found ->
+            case do_lookup(Mod, Key, [State#state.c, State#state.b, State#state.a]) of
+                not_found when Next =:= undefined ->
                     plain_rpc:send_reply(From, not_found);
                 {found, Result} ->
                     plain_rpc:send_reply(From, {ok, Result});
-                {delegate, DelegatePid} ->
-                    DelegatePid ! Req
+                not_found ->
+                    Next ! Req
             end,
             main_loop(State);
 
         ?CAST(_From, {lookup, Key, ReplyFun})=Req ->
-            case do_lookup(Key, [State#state.c, State#state.b, State#state.a, Next]) of
-                not_found ->
+            case do_lookup(Mod, Key, [State#state.c, State#state.b, State#state.a]) of
+                not_found when Next =:= undefined ->
                     ReplyFun(not_found);
                 {found, Result} ->
                     ReplyFun({ok, Result});
-                {delegate, DelegatePid} ->
-                    DelegatePid ! Req
+                not_found ->
+                    Next ! Req
             end,
             main_loop(State);
 
@@ -310,7 +327,7 @@ main_loop(State = #state{ next=Next }) ->
 
             plain_rpc:send_reply(From, ok),
 
-            case hanoidb_reader:open(ToFileName, [random|State#state.opts]) of
+            case Mod:open_random_reader(ToFileName, [random|State#state.opts]) of
                 {ok, BT} ->
                     if SetPos == #state.b ->
                             check_begin_merge_then_loop(setelement(SetPos, State, BT));
@@ -406,9 +423,9 @@ main_loop(State = #state{ next=Next }) ->
             main_loop(State2#state{ step_next_ref=undefined });
 
         ?CALL(From, close) ->
-            close_if_defined(State#state.a),
-            close_if_defined(State#state.b),
-            close_if_defined(State#state.c),
+            close_if_defined(Mod, State#state.a),
+            close_if_defined(Mod, State#state.b),
+            close_if_defined(Mod, State#state.c),
             [stop_if_defined(PID) || PID <- [State#state.merge_pid | State#state.folding]],
 
             %% this is synchronous all the way down, because our
@@ -422,9 +439,9 @@ main_loop(State = #state{ next=Next }) ->
             {ok, closing};
 
         ?CALL(From, destroy) ->
-            destroy_if_defined(State#state.a),
-            destroy_if_defined(State#state.b),
-            destroy_if_defined(State#state.c),
+            destroy_if_defined(Mod,State#state.a),
+            destroy_if_defined(Mod,State#state.b),
+            destroy_if_defined(Mod,State#state.c),
             [stop_if_defined(PID) || PID <- [State#state.merge_pid | State#state.folding]],
 
             %% this is synchronous all the way down, because our
@@ -496,27 +513,27 @@ main_loop(State = #state{ next=Next }) ->
 
                     {_, undefined, undefined} ->
                         ARef = erlang:make_ref(),
-                        ok = do_range_fold(State#state.a, WorkerPID, ARef, Range),
+                        ok = do_range_fold(Mod,State#state.a, WorkerPID, ARef, Range),
                         [ARef|List];
 
                     {_, _, undefined} ->
                         BRef = erlang:make_ref(),
-                        ok = do_range_fold(State#state.b, WorkerPID, BRef, Range),
+                        ok = do_range_fold(Mod,State#state.b, WorkerPID, BRef, Range),
 
                         ARef = erlang:make_ref(),
-                        ok = do_range_fold(State#state.a, WorkerPID, ARef, Range),
+                        ok = do_range_fold(Mod,State#state.a, WorkerPID, ARef, Range),
 
                         [ARef,BRef|List];
 
                     {_, _, _} ->
                         CRef = erlang:make_ref(),
-                        ok = do_range_fold(State#state.c, WorkerPID, CRef, Range),
+                        ok = do_range_fold(Mod,State#state.c, WorkerPID, CRef, Range),
 
                         BRef = erlang:make_ref(),
-                        ok = do_range_fold(State#state.b, WorkerPID, BRef, Range),
+                        ok = do_range_fold(Mod,State#state.b, WorkerPID, BRef, Range),
 
                         ARef = erlang:make_ref(),
-                        ok = do_range_fold(State#state.a, WorkerPID, ARef, Range),
+                        ok = do_range_fold(Mod,State#state.a, WorkerPID, ARef, Range),
 
                         [ARef,BRef,CRef|List]
                 end,
@@ -542,9 +559,9 @@ main_loop(State = #state{ next=Next }) ->
                 undefined ->
                     main_loop(State2#state{ merge_pid=undefined });
                 CFile ->
-                    ok = hanoidb_reader:close(CFile),
+                    ok = Mod:close_random_reader(CFile),
                     ok = file:rename(filename("C", State2), filename("A", State2)),
-                    {ok, AFile} = hanoidb_reader:open(filename("A", State2), [random|State#state.opts]),
+                    {ok, AFile} = Mod:open_random_reader(filename("A", State2), [random|State#state.opts]),
                     main_loop(State2#state{ a = AFile, c = undefined, merge_pid=undefined })
             end;
 
@@ -565,7 +582,7 @@ main_loop(State = #state{ next=Next }) ->
             % then, rename M to A, and open it
             AFileName = filename("A",State2),
             ok = file:rename(MFileName, AFileName),
-            {ok, AFile} = hanoidb_reader:open(AFileName, [random|State#state.opts]),
+            {ok, AFile} = Mod:open_random_reader(AFileName, [random|State#state.opts]),
 
             % iff there is a C file, then move it to B position
             % TODO: consider recovery for this
@@ -573,9 +590,9 @@ main_loop(State = #state{ next=Next }) ->
                 undefined ->
                     main_loop(State2#state{ a=AFile, b=undefined, merge_pid=undefined });
                 CFile ->
-                    ok = hanoidb_reader:close(CFile),
+                    ok = Mod:close_random_reader(CFile),
                     ok = file:rename(filename("C", State2), filename("B", State2)),
-                    {ok, BFile} = hanoidb_reader:open(filename("B", State2), [random|State#state.opts]),
+                    {ok, BFile} = Mod:open_random_reader(filename("B", State2), [random|State#state.opts]),
                     check_begin_merge_then_loop(State2#state{ a=AFile, b=BFile, c=undefined,
                                                               merge_pid=undefined })
             end;
@@ -722,9 +739,9 @@ reply_step_ok(State) ->
     case State#state.step_caller of
         undefined ->
             ok;
-        _ ->
-            ?log("step_ok -> ~p", [State#state.step_caller]),
-            plain_rpc:send_reply(State#state.step_caller, step_ok)
+        Caller ->
+            ?log("step_ok -> ~p", [Caller]),
+            plain_rpc:send_reply(Caller, step_ok)
     end,
     State#state{ step_caller=undefined }.
 
@@ -738,27 +755,28 @@ total_unmerged(State) ->
 
 
 
-do_lookup(_Key, []) ->
+do_lookup(_, _Key, []) ->
     not_found;
-do_lookup(_Key, [Pid]) when is_pid(Pid) ->
-    {delegate, Pid};
-do_lookup(Key, [undefined|Rest]) ->
-    do_lookup(Key, Rest);
-do_lookup(Key, [BT|Rest]) ->
-    case hanoidb_reader:lookup(BT, Key) of
+do_lookup(Mod, Key, [undefined|Rest]) ->
+    do_lookup(Mod, Key, Rest);
+do_lookup(Mod, Key, [BT|Rest]) ->
+    case Mod:lookup(Key, BT) of
         {ok, ?TOMBSTONE} ->
             not_found;
         {ok, Result} ->
             {found, Result};
         not_found ->
-            do_lookup(Key, Rest)
+            do_lookup(Mod,Key, Rest)
     end.
 
-close_if_defined(undefined) -> ok;
-close_if_defined(BT)        -> hanoidb_reader:close(BT).
+close_if_defined(_, undefined) -> ok;
+close_if_defined(Mod, BT)        -> Mod:close_random_reader(BT).
 
-destroy_if_defined(undefined) -> ok;
-destroy_if_defined(BT)        -> hanoidb_reader:destroy(BT).
+destroy_if_defined(_, undefined) -> ok;
+destroy_if_defined(Mod, BT) ->
+    {ok, Name} = Mod:file_name(BT),
+    Mod:close_random_reader(BT),
+    file:delete(Name).
 
 stop_if_defined(undefined) -> ok;
 stop_if_defined(MergePid) when is_pid(MergePid) ->
@@ -785,10 +803,12 @@ begin_merge(State) ->
          try
                        ?log("merge begun~n", []),
 
-                       {ok, OutCount} = hanoidb_merger:merge(AFileName, BFileName, XFileName,
-                                                           ?BTREE_SIZE(State#state.level + 1),
-                                                           State#state.next =:= undefined,
-                                                           State#state.opts ),
+                       {ok, OutCount} = hanoidb_backend:merge(
+                                          State#state.backend,
+                                          AFileName, BFileName, XFileName,
+                                          ?BTREE_SIZE(State#state.level + 1),
+                                          State#state.next =:= undefined,
+                                          State#state.opts ),
 
                        Owner ! ?CAST(self(),{merge_done, OutCount, XFileName})
          catch
@@ -805,9 +825,10 @@ begin_merge(State) ->
 close_and_delete_a_and_b(State) ->
     AFileName = filename("A",State),
     BFileName = filename("B",State),
+    Mod = State#state.backend,
 
-    ok = hanoidb_reader:close(State#state.a),
-    ok = hanoidb_reader:close(State#state.b),
+    ok = Mod:close_random_reader(State#state.a),
+    ok = Mod:close_random_reader(State#state.b),
 
     ok = file:delete(AFileName),
     ok = file:delete(BFileName),
@@ -821,14 +842,15 @@ filename(PFX, State) ->
 
 start_range_fold(FileName, WorkerPID, Range, State) ->
     Owner = self(),
+    Mod = State#state.backend,
     PID = proc_lib:spawn( fun() ->
           try
               ?log("start_range_fold ~p on ~p -> ~p", [self(), FileName, WorkerPID]),
               erlang:link(WorkerPID),
-              {ok, File} = hanoidb_reader:open(FileName, [folding|State#state.opts]),
-              do_range_fold2(File, WorkerPID, self(), Range),
+              {ok, File} = Mod:open_random_reader(FileName, [folding|State#state.opts]),
+              do_range_fold2(Mod,File, WorkerPID, self(), Range),
               erlang:unlink(WorkerPID),
-              hanoidb_reader:close(File),
+              Mod:close_random_reader(File),
 
               %% this will release the pinning of the fold file
               Owner  ! {range_fold_done, self(), FileName},
@@ -840,12 +862,13 @@ start_range_fold(FileName, WorkerPID, Range, State) ->
                           end ),
     {ok, PID}.
 
--spec do_range_fold(BT        :: hanoidb_reader:read_file(),
+-spec do_range_fold(Mod       :: atom(),
+                    BT        :: hanoidb_backend:random_reader(),
                     WorkerPID :: pid(),
                     SelfOrRef :: pid() | reference(),
                     Range     :: #key_range{} ) -> ok.
-do_range_fold(BT, WorkerPID, SelfOrRef, Range) ->
-    case hanoidb_reader:range_fold(fun(Key,Value,_) ->
+do_range_fold(Mod, BT, WorkerPID, SelfOrRef, Range) ->
+    case Mod:range_fold(fun(Key,Value,_) ->
                                              WorkerPID ! {level_result, SelfOrRef, Key, Value},
                                              ok
                                      end,
@@ -863,12 +886,13 @@ do_range_fold(BT, WorkerPID, SelfOrRef, Range) ->
 
 -define(FOLD_CHUNK_SIZE, 100).
 
--spec do_range_fold2(BT        :: hanoidb_reader:read_file(),
+-spec do_range_fold2(Mod      :: atom(),
+                    BT        :: hanoidb_reader:read_file(),
                     WorkerPID :: pid(),
                     SelfOrRef :: pid() | reference(),
                     Range     :: #key_range{} ) -> ok.
-do_range_fold2(BT, WorkerPID, SelfOrRef, Range) ->
-    try hanoidb_reader:range_fold(fun(Key,Value,{0,KVs}) ->
+do_range_fold2(Mod, BT, WorkerPID, SelfOrRef, Range) ->
+    try Mod:range_fold(fun(Key,Value,{0,KVs}) ->
                                          send(WorkerPID, SelfOrRef, [{Key,Value}|KVs]),
                                          {?FOLD_CHUNK_SIZE-1, []};
                                     (Key,Value,{N,KVs}) ->

src/hanoidb_nursery.erl

@@ -99,7 +99,7 @@ read_nursery_from_log(Directory, MaxLevel, Config) ->
 -spec do_add(#nursery{}, binary(), binary()|?TOMBSTONE, non_neg_integer() | infinity, pid()) -> {ok, #nursery{}} | {full, #nursery{}}.
 do_add(Nursery, Key, Value, infinity, Top) ->
     do_add(Nursery, Key, Value, 0, Top);
-do_add(Nursery=#nursery{log_file=File, cache=Cache, total_size=TotalSize, count=Count, config=Config}, Key, Value, KeyExpiryTime, Top) ->
+do_add(Nursery=#nursery{log_file=File, cache=Cache, total_size=TotalSize, count=Count, config=Config}, Key, Value, KeyExpiryTime, Top) when is_integer(KeyExpiryTime) ->
     DatabaseExpiryTime = hanoidb:get_opt(expiry_secs, Config),
 
     {Data, Cache2} =
@@ -175,7 +175,7 @@ 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, backend=Backend }, TopLevel) ->
 
     hanoidb_util:ensure_expiry(Config),
 
@@ -189,16 +189,17 @@ 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} = Backend:open_batch_writer(BTreeFileName, [{size, ?BTREE_SIZE(?TOP_LEVEL)},
                                                            {compress, none} | Config]),
-            try
-                ok = gb_trees_ext:fold(fun(Key, Value, Acc) ->
-                                               ok = hanoidb_writer:add(BT, Key, Value),
-                                               Acc
-                                       end, ok, Cache)
-            after
-                ok = hanoidb_writer:close(BT)
-            end,
+
+            BT3 = gb_trees_ext:fold(fun(Key, {Value,Expiry}, BT1) ->
+                                            {ok, BT2} = Backend:write_next({Key,Value,Expiry}, BT1),
+                                            BT2;
+                                       (Key, Value, BT1) ->
+                                            {ok, BT2} = Backend:write_next({Key,Value,infinity}, BT1),
+                                            BT2
+                                    end, BT, Cache),
+            ok = Backend:close_batch_writer(BT3),
 
             %% Inject the B-Tree (blocking RPC)
             ok = hanoidb_level:inject(TopLevel, BTreeFileName),

src/hanoidb_reader.erl

@@ -33,7 +33,7 @@
 -define(ASSERT_WHEN(X), when X).
 
 -export([open/1, open/2,close/1,lookup/2,fold/3,range_fold/4, destroy/1]).
--export([first_node/1,next_node/1]).
+-export([first_node/1,next_node/1,file_name/1]).
 -export([serialize/1, deserialize/1]).
 
 -record(node, {level       :: non_neg_integer(),
@@ -61,6 +61,7 @@ open(Name, Config) ->
             ReadBufferSize = hanoidb:get_opt(read_buffer_size, Config, 512 * 1024),
             case file:open(Name, [raw,read,{read_ahead, ReadBufferSize},binary]) of
                 {ok, File} ->
+                    {ok, Pos} = file:position(File, ?FIRST_BLOCK_POS),
                     {ok, #index{file=File, name=Name, config=Config}};
                 {error, _}=Err ->
                     Err
@@ -99,6 +100,9 @@ open(Name, Config) ->
             {ok, #index{file=File, root=Root, bloom=Bloom, name=Name, config=Config}}
     end.
 
+file_name(#index{name=Name}) ->
+    {ok, Name}.
+
 destroy(#index{file=File, name=Name}) ->
     ok = file:close(File),
     file:delete(Name).
@@ -130,7 +134,9 @@ fold1(File,Fun,Acc0) ->
         eof ->
             Acc0;
         {ok, Node} ->
-            fold0(File,Fun,Node,Acc0)
+            fold0(File,Fun,Node,Acc0);
+        {error,_}=Err ->
+            exit(Err)
     end.
 
 -spec range_fold(function(), any(), #index{}, #key_range{}) ->
@@ -193,7 +199,10 @@ do_range_fold(Fun, Acc0, File, Range, undefined) ->
                 {stopped, Result} -> Result;
                 {ok, Acc1} ->
                     do_range_fold(Fun, Acc1, File, Range, undefined)
-            end
+            end;
+
+        {error,_}=Err ->
+            Err
     end;
 
 do_range_fold(Fun, Acc0, File, Range, N0) ->
@@ -230,7 +239,10 @@ do_range_fold(Fun, Acc0, File, Range, N0) ->
                 {stopped, Result} -> Result;
                 {ok, {N2, Acc1}} ->
                     do_range_fold(Fun, Acc1, File, Range, N2)
-            end
+            end;
+
+        {error,_}=Err ->
+            Err
     end.
 
 lookup_node(_File,_FromKey,#node{level=0},Pos) ->
@@ -269,7 +281,10 @@ next_node(#index{file=File}=_Index) ->
 %        {ok, #node{level=N}} when N>0 ->
 %            next_node(Index);
         eof ->
-            end_of_data
+            end_of_data;
+
+        {error,_}=Err ->
+            Err
     end.
 
 close(#index{file=undefined}) ->
@@ -413,6 +428,8 @@ next_leaf_node(File) ->
             hanoidb_util:decode_index_node(0, Data);
         {ok, <<Len:32/unsigned, _:16/unsigned>>} ->
             {ok, _} = file:position(File, {cur,Len-2}),
-            next_leaf_node(File)
+            next_leaf_node(File);
+        {error,_}=Err ->
+            Err
     end.