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Introduce 3rd file in each level to reduce worst-case

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Now, each level is comprised of 3 files,

   A=Oldest, B=Older, C=Old

As in [Overmars and Leeuwen, 1983]. As soon as we have A & B,
we initiate a merge, (to the M=New) file, i.e. we merge more
eagerly than previously.

Next step in this refactoring is to add a scheduler that enforces
some merge activity as part of a PUT.
This commit is contained in:
Kresten Krab Thorup 2012-04-19 16:07:11 +02:00
parent 4e53b0a083
commit 3d80b164d5
3 changed files with 146 additions and 52 deletions
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6
levelpresence.sh
View file

@ -11,6 +11,8 @@ function periodic() {
echo -n " "
elif ! [ -f "B-$i.data" ] ; then
echo -n "-"
elif ! [ -f "C-$i.data" ] ; then
echo -n "#"
elif ! [ -f "X-$i.data" ] ; then
echo -n "="
else
@ -32,8 +34,10 @@ function dynamic() {
s="$s "
elif ! [ -f "B-$i.data" ] ; then
s="$s-"
elif ! [ -f "X-$i.data" ] ; then
elif ! [ -f "C-$i.data" ] ; then
s="$s="
elif ! [ -f "X-$i.data" ] ; then
s="$s%"
else
s="$s*"
fi

187
src/lsm_btree_level.erl
View file

@ -25,7 +25,8 @@
-module(lsm_btree_level).
-author('Kresten Krab Thorup <krab@trifork.com>').
-include("lsm_btree.hrl").
-include("include/lsm_btree.hrl").
-include("src/lsm_btree.hrl").
%%
%% Manages a "pair" of lsm_index (or rathern, 0, 1 or 2), and governs
@ -46,7 +47,7 @@
-include_lib("kernel/include/file.hrl").
-record(state, {
a, b, next, dir, level, inject_done_ref, merge_pid, folding = []
a, b, c, next, dir, level, inject_done_ref, merge_pid, folding = []
}).
%%%%% PUBLIC OPERATIONS
@ -77,13 +78,13 @@ close(Ref) ->
async_range(Ref, FoldWorkerPID, Range) ->
proc_lib:spawn(fun() ->
{ok, Folders} = call(Ref, {init_range_fold, FoldWorkerPID, Range, []}),
{ok, Folders} = call(Ref, {init_snapshot_range_fold, FoldWorkerPID, Range, []}),
FoldWorkerPID ! {initialize, Folders}
end),
{ok, FoldWorkerPID}.
sync_range(Ref, FoldWorkerPID, Range) ->
{ok, Folders} = call(Ref, {sync_range_fold, FoldWorkerPID, Range, []}),
{ok, Folders} = call(Ref, {init_blocking_range_fold, FoldWorkerPID, Range, []}),
FoldWorkerPID ! {initialize, Folders},
{ok, FoldWorkerPID}.
@ -123,29 +124,49 @@ reply({PID,Ref}, Reply) ->
initialize(State) ->
try
initialize2(State)
catch
Class:Ex ->
error_logger:error_msg("crash: ~p:~p ~p~n", [Class,Ex,erlang:get_stacktrace()])
end.
initialize2(State) ->
% error_logger:info_msg("in ~p level=~p~n", [self(), State]),
AFileName = filename("A",State),
BFileName = filename("B",State),
CFileName = filename("C",State),
MFileName = filename("M",State),
%% remove old merge file
file:delete( filename("X",State)),
%% remove old fold files (hard links to A/B used during fold)
%% remove old fold files (hard links to A/B/C used during fold)
file:delete( filename("AF",State)),
file:delete( filename("BF",State)),
file:delete( filename("CF",State)),
case file:read_file_info(CFileName) of
case file:read_file_info(MFileName) of
{ok, _} ->
%% recover from post-merge crash
file:delete(AFileName),
file:delete(BFileName),
ok = file:rename(CFileName, AFileName),
ok = file:rename(MFileName, AFileName),
{ok, BT} = lsm_btree_reader:open(CFileName, random),
main_loop(State#state{ a= BT, b=undefined });
{ok, BT} = lsm_btree_reader:open(AFileName, random),
case file:read_file_info(CFileName) of
{ok, _} ->
file:rename(CFileName, BFileName),
{ok, BT2} = lsm_btree_reader:open(BFileName, random),
check_begin_merge_then_loop(State#state{ a= BT, b=BT2 });
{error, enoent} ->
main_loop(State#state{ a= BT, b=undefined })
end;
{error, enoent} ->
case file:read_file_info(BFileName) of
@ -153,7 +174,14 @@ initialize(State) ->
{ok, BT1} = lsm_btree_reader:open(AFileName, random),
{ok, BT2} = lsm_btree_reader:open(BFileName, random),
check_begin_merge_then_loop(State#state{ a=BT1, b=BT2 });
case file:read_file_info(CFileName) of
{ok, _} ->
{ok, BT3} = lsm_btree_reader:open(CFileName, random);
{error, enoent} ->
BT3 = undefined
end,
check_begin_merge_then_loop(State#state{ a=BT1, b=BT2, c=BT3 });
{error, enoent} ->
@ -179,7 +207,7 @@ main_loop(State = #state{ next=Next }) ->
Parent = plain_fsm:info(parent),
receive
?REQ(From, {lookup, Key})=Req ->
case do_lookup(Key, [State#state.b, State#state.a, Next]) of
case do_lookup(Key, [State#state.c, State#state.b, State#state.a, Next]) of
not_found ->
reply(From, not_found);
{found, Result} ->
@ -189,13 +217,17 @@ main_loop(State = #state{ next=Next }) ->
end,
main_loop(State);
?REQ(From, {inject, FileName}) when State#state.b == undefined ->
if State#state.a == undefined ->
?REQ(From, {inject, FileName}) when State#state.c == undefined ->
case {State#state.a, State#state.b} of
{undefined, undefined} ->
ToFileName = filename("A",State),
SetPos = #state.a;
true ->
{_, undefined} ->
ToFileName = filename("B",State),
SetPos = #state.b
SetPos = #state.b;
{_, _} ->
ToFileName = filename("C",State),
SetPos = #state.c
end,
ok = file:rename(FileName, ToFileName),
{ok, BT} = lsm_btree_reader:open(ToFileName, random),
@ -205,6 +237,7 @@ main_loop(State = #state{ next=Next }) ->
?REQ(From, close) ->
close_if_defined(State#state.a),
close_if_defined(State#state.b),
close_if_defined(State#state.c),
stop_if_defined(State#state.merge_pid),
reply(From, ok),
@ -217,69 +250,94 @@ main_loop(State = #state{ next=Next }) ->
end,
ok;
?REQ(From, {init_range_fold, WorkerPID, Range, List}) when State#state.folding == [] ->
?REQ(From, {init_snapshot_range_fold, WorkerPID, Range, List}) when State#state.folding == [] ->
case {State#state.a, State#state.b} of
{undefined, undefined} ->
NewFolding = [],
case {State#state.a, State#state.b, State#state.c} of
{undefined, undefined, undefined} ->
FoldingPIDs = [],
NextList = List;
{_, undefined} ->
{_, undefined, undefined} ->
ok = file:make_link(filename("A", State), filename("AF", State)),
{ok, PID0} = start_range_fold(filename("AF",State), WorkerPID, Range),
NextList = [PID0|List],
NewFolding = [PID0];
FoldingPIDs = [PID0];
{_, _} ->
{_, _, undefined} ->
ok = file:make_link(filename("A", State), filename("AF", State)),
{ok, PID0} = start_range_fold(filename("AF",State), WorkerPID, Range),
{ok, PIDA} = start_range_fold(filename("AF",State), WorkerPID, Range),
ok = file:make_link(filename("B", State), filename("BF", State)),
{ok, PID1} = start_range_fold(filename("BF",State), WorkerPID, Range),
{ok, PIDB} = start_range_fold(filename("BF",State), WorkerPID, Range),
NextList = [PID1,PID0|List],
NewFolding = [PID1,PID0]
NextList = [PIDA,PIDB|List],
FoldingPIDs = [PIDB,PIDA];
{_, _, _} ->
ok = file:make_link(filename("A", State), filename("AF", State)),
{ok, PIDA} = start_range_fold(filename("AF",State), WorkerPID, Range),
ok = file:make_link(filename("B", State), filename("BF", State)),
{ok, PIDB} = start_range_fold(filename("BF",State), WorkerPID, Range),
ok = file:make_link(filename("C", State), filename("CF", State)),
{ok, PIDC} = start_range_fold(filename("CF",State), WorkerPID, Range),
NextList = [PIDA,PIDB,PIDC|List],
FoldingPIDs = [PIDC,PIDB,PIDA]
end,
case Next of
undefined ->
reply(From, {ok, lists:reverse(NextList)});
_ ->
Next ! ?REQ(From, {init_range_fold, WorkerPID, Range, NextList})
Next ! ?REQ(From, {init_snapshot_range_fold, WorkerPID, Range, NextList})
end,
main_loop(State#state{ folding = NewFolding });
main_loop(State#state{ folding = FoldingPIDs });
{range_fold_done, PID, [_,$F|_]=FoldFileName} ->
ok = file:delete(FoldFileName),
main_loop(State#state{ folding = lists:delete(PID,State#state.folding) });
?REQ(From, {sync_range_fold, WorkerPID, Range, List}) ->
?REQ(From, {init_blocking_range_fold, WorkerPID, Range, List}) ->
case {State#state.a, State#state.b} of
{undefined, undefined} ->
case {State#state.a, State#state.b, State#state.c} of
{undefined, undefined, undefined} ->
RefList = List;
{_, undefined} ->
{_, undefined, undefined} ->
ARef = erlang:make_ref(),
ok = do_range_fold(State#state.a, WorkerPID, ARef, Range),
RefList = [ARef|List];
{_, _} ->
{_, _, undefined} ->
BRef = erlang:make_ref(),
ok = do_range_fold(State#state.b, WorkerPID, BRef, Range),
ARef = erlang:make_ref(),
ok = do_range_fold(State#state.a, WorkerPID, ARef, Range),
RefList = [ARef,BRef|List]
RefList = [ARef,BRef|List];
{_, _, _} ->
CRef = erlang:make_ref(),
ok = do_range_fold(State#state.c, WorkerPID, CRef, Range),
BRef = erlang:make_ref(),
ok = do_range_fold(State#state.b, WorkerPID, BRef, Range),
ARef = erlang:make_ref(),
ok = do_range_fold(State#state.a, WorkerPID, ARef, Range),
RefList = [ARef,BRef,CRef|List]
end,
case Next of
undefined ->
reply(From, {ok, lists:reverse(RefList)});
_ ->
Next ! ?REQ(From, {sync_range_fold, WorkerPID, Range, RefList})
Next ! ?REQ(From, {init_blocking_range_fold, WorkerPID, Range, RefList})
end,
main_loop(State);
@ -291,19 +349,29 @@ main_loop(State = #state{ next=Next }) ->
%%
{merge_done, Count, OutFileName} when Count =< ?BTREE_SIZE(State#state.level) ->
% first, rename the tmp file to C, so recovery will pick it up
CFileName = filename("C",State),
ok = file:rename(OutFileName, CFileName),
% first, rename the tmp file to M, so recovery will pick it up
MFileName = filename("M",State),
ok = file:rename(OutFileName, MFileName),
% then delete A and B (if we crash now, C will become the A file)
{ok, State2} = close_a_and_b(State),
{ok, State2} = close_and_delete_a_and_b(State),
% then, rename C to A, and open it
% then, rename M to A, and open it
AFileName = filename("A",State2),
ok = file:rename(CFileName, AFileName),
ok = file:rename(MFileName, AFileName),
{ok, BT} = lsm_btree_reader:open(AFileName, random),
main_loop(State2#state{ a=BT, b=undefined, merge_pid=undefined });
% iff there is a C file, then move it to B position
% TODO: consider recovery for this
case State#state.c of
undefined ->
main_loop(State2#state{ a=BT, b=undefined, merge_pid=undefined });
TreeFile ->
file:rename(filename("C",State2), filename("B", State2)),
check_begin_merge_then_loop(State2#state{ a=BT, b=TreeFile, c=undefined,
merge_pid=undefined })
end;
%%
%% We need to push the output of merging to the next level
@ -317,6 +385,8 @@ main_loop(State = #state{ next=Next }) ->
State
end,
%% no need to rename it since we don't accept new injects
MRef = send_request(State1#state.next, {inject, OutFileName}),
main_loop(State1#state{ inject_done_ref = MRef, merge_pid=undefined });
@ -325,14 +395,25 @@ main_loop(State = #state{ next=Next }) ->
%%
?REPLY(MRef, ok) when MRef =:= State#state.inject_done_ref ->
erlang:demonitor(MRef, [flush]),
{ok, State2} = close_a_and_b(State),
main_loop(State2#state{ inject_done_ref=undefined });
{ok, State2} = close_and_delete_a_and_b(State),
% if there is a "C" file, then move it to "A" position.
case State2#state.c of
undefined ->
State3=State2;
TreeFile ->
%% TODO: on what OS's is it ok to rename an open file?
ok = file:rename(filename("C", State2), filename("A", State2)),
State3 = State2#state{ a = TreeFile, b=undefined, c=undefined }
end,
main_loop(State3#state{ inject_done_ref=undefined });
%%
%% Our successor died!
%%
{'DOWN', MRef, _, _, Reason} when MRef =:= State#state.inject_done_ref ->
exit(Reason);
{'DOWN', MRef, _, _, Reason} when MRef =:= State#state.inject_done_ref ->
exit(Reason);
%% gen_fsm handling
{system, From, Req} ->
@ -404,7 +485,7 @@ begin_merge(State) ->
{ok, MergePID}.
close_a_and_b(State) ->
close_and_delete_a_and_b(State) ->
AFileName = filename("A",State),
BFileName = filename("B",State),
@ -435,19 +516,23 @@ start_range_fold(FileName, WorkerPID, Range) ->
end ),
{ok, PID}.
do_range_fold(BT, WorkerPID, Self, Range) ->
-spec do_range_fold(BT :: lsm_btree_reader:read_file(),
WorkerPID :: pid(),
SelfOrRef :: pid() | reference(),
Range :: #btree_range{} ) -> ok.
do_range_fold(BT, WorkerPID, SelfOrRef, Range) ->
case lsm_btree_reader:range_fold(fun(Key,Value,_) ->
WorkerPID ! {level_result, Self, Key, Value},
WorkerPID ! {level_result, SelfOrRef, Key, Value},
ok
end,
ok,
BT,
Range) of
{limit, _, LastKey} ->
WorkerPID ! {level_limit, Self, LastKey};
WorkerPID ! {level_limit, SelfOrRef, LastKey};
{done, _} ->
%% tell fold merge worker we're done
WorkerPID ! {level_done, Self}
WorkerPID ! {level_done, SelfOrRef}
end,
ok.

5
src/lsm_btree_reader.erl
View file

@ -35,9 +35,14 @@
-record(node, { level, members=[] }).
-record(index, {file, root, bloom}).
-type read_file() :: #index{}.
-spec open(Name::string()) -> read_file().
open(Name) ->
open(Name, random).
-spec open(Name::string(), sequential|random) -> read_file().
%% this is how to open a btree for sequential scanning (merge, fold)
open(Name, sequential) ->
{ok, File} = file:open(Name, [raw,read,{read_ahead, 1024 * 512},binary]),