aboutsummaryrefslogblamecommitdiffstats
path: root/lib/stdlib/src/dets_v8.erl
blob: 3e962a1c8b1204d99969fabd893c11af093e182d (plain) (tree)
1
2
3
4
5
6
7
8
9
10
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
                   
  
                                                        
  



                                                                      
  


                                                                         
  





                                                                      
                                          











































































































































                                                                             
                                                              






























                                                                      










































































































                                                                             

                                                                            






                                                               
                                                      










                                                                           
                                     
















































































                                                                              
                                            





























































































































































































































































































































































































































































































































































































































































                                                                               
                                              
                                                               
                                                            
                     
                                                              
                                                                
                                                          











                                                                       
                          






















































































































































































                                                                               
                                              



































                                                                               
                                           
                                         
                                                
                                                     
                                                                  

                                                           
                                                         

                                                                          
                                                          

                                                     
                                                 

                                                                      
                              










































































































































































































































































                                                                             
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2001-2011. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
-module(dets_v8).

%% Dets files, implementation part. This module handles versions up to
%% and including 8(c). To be called from dets.erl only.

-export([mark_dirty/1, read_file_header/2,
         check_file_header/2, do_perform_save/1, initiate_file/11,
         init_freelist/2, fsck_input/4,
         bulk_input/3, output_objs/4, write_cache/1, may_grow/3,
         find_object/2, re_hash/2, slot_objs/2, scan_objs/8,
         db_hash/2, no_slots/1, table_parameters/1]).

-export([file_info/1, v_segments/1]).

-export([cache_segps/3]).

%% For backward compatibility.
-export([sz2pos/1]).

-compile({inline, [{sz2pos,1},{scan_skip,7}]}).
-compile({inline, [{skip_bytes,5}, {get_segp,1}]}).
-compile({inline, [{wl_lookup,5}]}).
-compile({inline, [{actual_seg_size,0}]}).

-include("dets.hrl").

%%  The layout of the file is :
%%
%%   bytes   decsription
%%  ---------------------- File header
%%    4      FreelistsPointer
%%    4      Cookie
%%    4      ClosedProperly (pos=8)
%%    4      Type (pos=12)
%%    4      Version (pos=16)
%%    4      M
%%    4      Next
%%    4      KeyPos
%%    4      NoObjects
%%    4      N
%%  ------------------ end of file header
%%    4*8192 SegmentArray
%%  ------------------
%%    4*256  First segment
%%  ----------------------------- This is BASE.
%%    ???    Objects (free and alive)
%%    4*256  Second segment (2 kB now, due to a bug)
%%    ???    Objects (free and alive)
%%    ... more objects and segments ...
%%  -----------------------------
%%    ???    Free lists
%%  -----------------------------
%%    4      File size, in bytes. 

%%  The first slot (0) in the segment array always points to the
%%  pre-allocated first segment.
%%  Before we can find an object we must find the slot where the
%%  object resides. Each slot is a (possibly empty) list (or chain) of
%%  objects that hash to the same slot. If the value stored in the
%%  slot is zero, the slot chain is empty. If the slot value is
%%  non-zero, the value points to a position in the file where the
%%  chain starts. Each object in a chain has the following layout:
%%
%%   bytes  decsription
%%  --------------------
%%    4     Pointer to the next object of the chain.
%%    4     Size of the object in bytes (Sz).
%%    4     Status  (FREE or ACTIVE)
%%    Sz    Binary representing the object
%%
%%  The status field is used while repairing a file (but not next or size).
%%
%%|---------------|
%%|      head     |
%%|       	  |
%%|               |
%%|_______________|
%%|		  |------|
%%|___seg ptr1____|      |
%%|		  |      |
%%|__ seg ptr 2___|      |
%%|               |      |    segment 1
%%|	....	  |      V _____________
%%			 |		|
%%			 |		|
%%			 |___slot 0 ____|
%%                       |              |
%%                       |___slot 1 ____|-----|
%%			 |		|     |
%%			 |   .....	|     |  1:st obj in slot 1
%%					      V  segment 1
%%						|-----------|
%%						|  next     |
%%						|___________|
%%						|  size     |
%%						|___________|
%%						|  status   |
%%						|___________|
%%						|	    |
%%						|           |
%%						|   obj     |
%%						|           |

%%%
%%% File header
%%%

-define(HEADSZ, 40).          % The size of the file header, in bytes.
-define(SEGSZ, 256).          % Size of a segment, in words.
-define(SEGSZ_LOG2, 8).
-define(SEGARRSZ, 8192).      % Maximal number of segments.
-define(SEGADDR(SegN), (?HEADSZ + (4 * (SegN)))).
-define(BASE, ?SEGADDR((?SEGSZ + ?SEGARRSZ))).
-define(MAXOBJS, (?SEGSZ * ?SEGARRSZ)). % 2 M objects

-define(SLOT2SEG(S), ((S) bsr ?SEGSZ_LOG2)).

%% BIG is used for hashing. BIG must be greater than the maximum
%% number of slots, currently MAXOBJS.
-define(BIG, 16#ffffff).

%% Hard coded positions into the file header:
-define(FREELIST_POS, 0).
-define(CLOSED_PROPERLY_POS, 8).
-define(D_POS, 20).
-define(NO_OBJECTS_POS, (?D_POS + 12)).

%% The version of a dets file is indicated by the ClosedProperly
%% field. Version 6 was used in the R1A release, and version 7 in the
%% R1B release up to and including the R3B01 release. Both version 6
%% and version 7 indicate properly closed files by the value
%% CLOSED_PROPERLY.
%%
%% The current version, 8, has three sub-versions:
%%
%% - 8(a), indicated by the value CLOSED_PROPERLY (same as in versions 6 
%%         and 7), introduced in R3B02;
%% - 8(b), indicated by the value CLOSED_PROPERLY2(_NEED_COMPACTING),
%%         introduced in R5A and used up to and including R6A;
%% - 8(c), indicated by the value CLOSED_PROPERLY_NEW_HASH(_NEED_COMPACTING),
%%         in use since R6B.
%%
%% The difference between the 8(a) and the 8(b) versions is the format
%% used for free lists saved on dets files.
%% The 8(c) version uses a different hashing algorithm, erlang:phash
%% (former versions use erlang:hash).
%% Version 8(b) files are only converted to version 8(c) if repair is
%% done, so we need compatibility with 8(b) for a _long_ time.
%%
%% There are known bugs due to the fact that keys and objects are
%% sometimes compared (==) and sometimes matched (=:=). The version
%% used by default (9, see dets_v9.erl) does not have this problem.

-define(NOT_PROPERLY_CLOSED,0).
-define(CLOSED_PROPERLY,1).
-define(CLOSED_PROPERLY2,2).
-define(CLOSED_PROPERLY2_NEED_COMPACTING,3).
-define(CLOSED_PROPERLY_NEW_HASH,4).
-define(CLOSED_PROPERLY_NEW_HASH_NEED_COMPACTING,5).

-define(FILE_FORMAT_VERSION, 8).
-define(CAN_BUMP_BY_REPAIR, [6, 7]).
-define(CAN_CONVERT_FREELIST, [8]).

%%%
%%% Object header (next, size, status).
%%%

-define(OHDSZ, 12).         % The size of the object header, in bytes.
-define(STATUS_POS, 8).     % Position of the status field.

%% The size of each object is a multiple of 16.
%% BUMP is used when repairing files.
-define(BUMP, 16).

-define(ReadAhead, 512).

%%-define(DEBUGF(X,Y), io:format(X, Y)).
-define(DEBUGF(X,Y), void).

%% -> ok | throw({NewHead,Error})
mark_dirty(Head) ->
    Dirty = [{?CLOSED_PROPERLY_POS, <<?NOT_PROPERLY_CLOSED:32>>}],
    dets_utils:pwrite(Head, Dirty),
    dets_utils:sync(Head),
    dets_utils:position(Head, Head#head.freelists_p),
    dets_utils:truncate(Head, cur).

%% -> {ok, head()} | throw(Error)
initiate_file(Fd, Tab, Fname, Type, Kp, MinSlots, MaxSlots, 
		Ram, CacheSz, Auto, _DoInitSegments) ->
    Freelist = 0,
    Cookie = ?MAGIC,
    ClosedProperly = ?NOT_PROPERLY_CLOSED, % immediately overwritten
    Version = ?FILE_FORMAT_VERSION,
    Factor = est_no_segments(MinSlots),
    N = 0,
    M = Next = ?SEGSZ * Factor,
    NoObjects = 0,
    dets_utils:pwrite(Fd, Fname, 0, 
                      <<Freelist:32,
                      Cookie:32,
                      ClosedProperly:32,
                      (dets_utils:type_to_code(Type)):32,
                      Version:32,
                      M:32,
                      Next:32,
                      Kp:32,
                      NoObjects:32,
                      N:32,
		      0:(?SEGARRSZ*4)/unit:8, % Initialize SegmentArray
		      0:(?SEGSZ*4)/unit:8>>), % Initialize first segment
    %% We must set the first slot of the segment pointer array to
    %% point to the first segment
    Pos = ?SEGADDR(0),
    SegP = (?HEADSZ + (4 * ?SEGARRSZ)),
    dets_utils:pwrite(Fd, Fname, Pos, <<SegP:32>>),
    segp_cache(Pos, SegP),

    Ftab = dets_utils:init_alloc(?BASE),
    H0 = #head{freelists=Ftab, fptr = Fd, base = ?BASE},
    {H1, Ws} = init_more_segments(H0, 1, Factor, undefined, []),

    %% This is not optimal but simple: always initiate the segments.
    dets_utils:pwrite(Fd, Fname, Ws),

    %% Return a new nice head structure
    Head = #head{
      m  = M,
      m2 = M * 2,
      next = Next,
      fptr = Fd,
      no_objects = NoObjects,
      n = N,
      type = Type,
      update_mode = dirty,
      freelists = H1#head.freelists,
      auto_save = Auto,
      hash_bif = phash,
      keypos = Kp,
      min_no_slots = Factor * ?SEGSZ,
      max_no_slots = no_segs(MaxSlots) * ?SEGSZ,
      
      ram_file = Ram, 
      filename = Fname, 
      name = Tab,
      cache = dets_utils:new_cache(CacheSz),
      version = Version,
      bump = ?BUMP,
      base = ?BASE,
      mod = ?MODULE
     },
    {ok, Head}.

est_no_segments(MinSlots) when 1 + ?SLOT2SEG(MinSlots) > ?SEGARRSZ ->
    ?SEGARRSZ;
est_no_segments(MinSlots) ->
    1 + ?SLOT2SEG(MinSlots).

init_more_segments(Head, SegNo, Factor, undefined, Ws) when SegNo < Factor ->
    init_more_segments(Head, SegNo, Factor, seg_zero(), Ws);
init_more_segments(Head, SegNo, Factor, SegZero, Ws) when SegNo < Factor ->
    {NewHead, W} = allocate_segment(Head, SegZero, SegNo),
    init_more_segments(NewHead, SegNo+1, Factor, SegZero, W++Ws);
init_more_segments(Head, _SegNo, _Factor, _SegZero, Ws) ->
    {Head, Ws}.

allocate_segment(Head, SegZero, SegNo) ->
    %% may throw error:
    {NewHead, Segment, _} = dets_utils:alloc(Head, 4 * ?SEGSZ),
    InitSegment = {Segment, SegZero},
    Pos = ?SEGADDR(SegNo),
    segp_cache(Pos, Segment),
    SegPointer = {Pos, <<Segment:32>>},
    {NewHead, [InitSegment, SegPointer]}.

%% Read free lists (using a Buddy System) from file. 
init_freelist(Head, {convert_freelist,_Version}) ->
    %% This function converts the saved freelist of the form
    %% [{Slot1,Addr1},{Addr1,Addr2},...,{AddrN,0},{Slot2,Addr},...]
    %% i.e each slot is a linked list which ends with a 0.
    %% This is stored in a bplus_tree per Slot.
    %% Each Slot is a position in a tuple.

    Ftab = dets_utils:empty_free_lists(),
    Pos = Head#head.freelists_p,
    case catch prterm(Head, Pos, ?OHDSZ) of
	{0, _Sz, Term}  ->
	    FreeList1 = lists:reverse(Term),
            FreeList = dets_utils:init_slots_from_old_file(FreeList1, Ftab),
            Head#head{freelists = FreeList, base = ?BASE};
	_ ->
	    throw({error, {bad_freelists, Head#head.filename}})
    end;
init_freelist(Head, _) ->
    %% bplus_tree stored as is
    Pos = Head#head.freelists_p,
    case catch prterm(Head, Pos, ?OHDSZ) of
	{0, _Sz, Term}  ->
            Head#head{freelists = Term, base = ?BASE};
	_ ->
	    throw({error, {bad_freelists, Head#head.filename}})
    end.

%% -> {ok, Fd, fileheader()} | throw(Error)
read_file_header(Fd, FileName) ->
    {ok, Bin} = dets_utils:pread_close(Fd, FileName, 0, ?HEADSZ),
    [Freelist, Cookie, CP, Type2, Version, M, Next, Kp, NoObjects, N] = 
	bin2ints(Bin),
    {ok, EOF} = dets_utils:position_close(Fd, FileName, eof),
    {ok, <<FileSize:32>>} = dets_utils:pread_close(Fd, FileName, EOF-4, 4),
    FH = #fileheader{freelist = Freelist,
                     fl_base = ?BASE,
		     cookie = Cookie,
		     closed_properly = CP,
		     type = dets_utils:code_to_type(Type2),
		     version = Version,
		     m = M,
		     next = Next,
		     keypos = Kp,
		     no_objects = NoObjects,
		     min_no_slots = ?DEFAULT_MIN_NO_SLOTS,
		     max_no_slots = ?DEFAULT_MAX_NO_SLOTS,
		     trailer = FileSize,
		     eof = EOF,
		     n = N,
		     mod = ?MODULE},
    {ok, Fd, FH}.

%% -> {ok, head(), ExtraInfo} | {error, Reason} (Reason lacking file name)
%% ExtraInfo = {convert_freelist, Version} | true | need_compacting 
check_file_header(FH, Fd) ->
    Test = 
	if
	    FH#fileheader.cookie =/= ?MAGIC ->
		{error, not_a_dets_file};
	    FH#fileheader.type =:= badtype ->
		{error, invalid_type_code};
	    FH#fileheader.version =/= ?FILE_FORMAT_VERSION -> 
		case lists:member(FH#fileheader.version,
                                  ?CAN_BUMP_BY_REPAIR) of
		    true ->
			{error, version_bump};
		    false ->
			{error, bad_version}
		end;
	    FH#fileheader.trailer =/= FH#fileheader.eof ->
		{error, not_closed};
	    FH#fileheader.closed_properly =:= ?CLOSED_PROPERLY ->
		case lists:member(FH#fileheader.version,
				  ?CAN_CONVERT_FREELIST) of
		    true ->
			{ok, {convert_freelist, FH#fileheader.version}, hash};
		    false ->
			{error, not_closed} % should not happen
		end;
	    FH#fileheader.closed_properly =:= ?CLOSED_PROPERLY2 ->
		{ok, true, hash};
	    FH#fileheader.closed_properly =:= 
	          ?CLOSED_PROPERLY2_NEED_COMPACTING  ->
		{ok, need_compacting, hash};
	    FH#fileheader.closed_properly =:= ?CLOSED_PROPERLY_NEW_HASH ->
		{ok, true, phash};
	    FH#fileheader.closed_properly =:= 
	         ?CLOSED_PROPERLY_NEW_HASH_NEED_COMPACTING  ->
		{ok, need_compacting, phash};
	    FH#fileheader.closed_properly =:= ?NOT_PROPERLY_CLOSED ->
		{error, not_closed};
	    FH#fileheader.closed_properly > 
	         ?CLOSED_PROPERLY_NEW_HASH_NEED_COMPACTING ->
		{error, not_closed};
	    true ->
		{error, not_a_dets_file}
	end,
    case Test of
	{ok, ExtraInfo, HashAlg} ->
	    H = #head{
	      m = FH#fileheader.m,
	      m2 = FH#fileheader.m * 2,
	      next = FH#fileheader.next,
	      fptr = Fd,
	      no_objects= FH#fileheader.no_objects,
	      n = FH#fileheader.n,
	      type = FH#fileheader.type,
	      update_mode = saved,
	      auto_save = infinity,             % not saved on file
	      fixed = false,			% not saved on file
	      freelists_p = FH#fileheader.freelist,
	      hash_bif = HashAlg,
	      keypos = FH#fileheader.keypos,
	      min_no_slots = FH#fileheader.min_no_slots,
	      max_no_slots = FH#fileheader.max_no_slots,
	      version = ?FILE_FORMAT_VERSION,
	      mod = ?MODULE,
	      bump = ?BUMP,
	      base = FH#fileheader.fl_base},
	    {ok, H, ExtraInfo};
	Error ->
	    Error
    end.

cache_segps(Fd, FileName, M) ->
    NSegs = no_segs(M),
    {ok, Bin} = dets_utils:pread_close(Fd, FileName, ?HEADSZ, 4 * NSegs),
    Fun = fun(S, P) -> segp_cache(P, S), P+4 end,
    lists:foldl(Fun, ?HEADSZ, bin2ints(Bin)).

no_segs(NoSlots) ->
    ?SLOT2SEG(NoSlots - 1) + 1.

bin2ints(<<Int:32, B/binary>>) ->
    [Int | bin2ints(B)];
bin2ints(<<>>) ->
    [].

%%%
%%% Repair, conversion and initialization of a dets file.
%%%

bulk_input(Head, InitFun, Cntrs) ->
    bulk_input(Head, InitFun, Cntrs, make_ref()).

bulk_input(Head, InitFun, Cntrs, Ref) ->
    fun(close) ->
	    ok;
       (read) ->
	    case catch {Ref, InitFun(read)} of
		{Ref, end_of_input} ->
		    end_of_input;
		{Ref, {L0, NewInitFun}} when is_list(L0), 
                                             is_function(NewInitFun) ->
		    Kp = Head#head.keypos,
		    case catch bulk_objects(L0, Head, Cntrs, Kp, []) of
			{'EXIT', _Error} ->
			    _ = (catch NewInitFun(close)),
			    {error, invalid_objects_list};
			L ->
			    {L, bulk_input(Head, NewInitFun, Cntrs, Ref)}
		    end;
		{Ref, Value} ->
		    {error, {init_fun, Value}};
		Error ->
		    throw({thrown, Error})
	    end
    end.

bulk_objects([T | Ts], Head, Cntrs, Kp, L) ->
    BT = term_to_binary(T),
    Sz = byte_size(BT),
    LogSz = sz2pos(Sz+?OHDSZ),
    count_object(Cntrs, LogSz),
    Key = element(Kp, T),
    bulk_objects(Ts, Head, Cntrs, Kp, [make_object(Head, Key, LogSz, BT) | L]);
bulk_objects([], _Head, _Cntrs, _Kp, L) ->
    L.

-define(FSCK_SEGMENT, 10000).

-define(DCT(D, CT), [D | CT]).

-define(VNEW(N, E), erlang:make_tuple(N, E)).
-define(VSET(I, V, E), setelement(I, V, E)).
-define(VGET(I, V), element(I, V)).

%% OldVersion not used, assuming later versions have been converted already.
output_objs(OldVersion, Head, SlotNumbers, Cntrs) ->
    fun(close) ->
	    {ok, 0, Head};
       ([]) ->
	    output_objs(OldVersion, Head, SlotNumbers, Cntrs);
       (L) ->
	    %% Descending sizes.
	    Count = lists:sort(ets:tab2list(Cntrs)),
	    RCount = lists:reverse(Count),
	    NoObjects = lists:foldl(fun({_Sz,No}, A) -> A + No end, 0, Count),
	    {_, MinSlots, _} = SlotNumbers,
	    if
		%% Using number of objects for bags and duplicate bags
		%% is not ideal; number of (unique) keys should be
		%% used instead. The effect is that there will be more
		%% segments than "necessary".
		MinSlots =/= bulk_init,
		abs(?SLOT2SEG(NoObjects) - ?SLOT2SEG(MinSlots)) > 5,
		(NoObjects < ?MAXOBJS) ->
		    {try_again, NoObjects};
		true ->
                    Head1 = Head#head{no_objects = NoObjects},
		    SegSz = actual_seg_size(),
		    {_, End, _} = dets_utils:alloc(Head, SegSz-1),
		    %% Now {LogSize,NoObjects} in Cntrs is replaced by
		    %% {LogSize,Position,{FileName,FileDescriptor},NoObjects}.
		    {Head2, CT} = allocate_all_objects(Head1, RCount, Cntrs),
		    [E | Es] = bin2term(L, []),
		    {NE, Acc, DCT1} = 
			output_slots(E, Es, [E], Head2, ?DCT(0, CT)),
		    NDCT = write_all_sizes(DCT1, Cntrs),
		    Max = ets:info(Cntrs, size),
                    output_objs2(NE, Acc, Head2, Cntrs, NDCT, End, Max,Max)
	    end
    end.

output_objs2(E, Acc, Head, Cntrs, DCT, End, 0, MaxNoChunks) ->
    NDCT = write_all_sizes(DCT, Cntrs),
    output_objs2(E, Acc, Head, Cntrs, NDCT, End, MaxNoChunks, MaxNoChunks);
output_objs2(E, Acc, Head, Cntrs, DCT, End, ChunkI, MaxNoChunks) ->
    fun(close) ->
	    DCT1 = output_slot(Acc, Head, DCT),
	    NDCT = write_all_sizes(DCT1, Cntrs),
	    ?DCT(NoDups, CT) = NDCT,
	    [SegAddr | []] = ?VGET(tuple_size(CT), CT),
            FinalZ = End - SegAddr,
            [{?FSCK_SEGMENT, _, {FileName, Fd}, _}] = 
		ets:lookup(Cntrs, ?FSCK_SEGMENT),
	    ok = dets_utils:fwrite(Fd, FileName, 
				   dets_utils:make_zeros(FinalZ)),
            NewHead = Head#head{no_objects = Head#head.no_objects - NoDups},
	    {ok, NoDups, NewHead};
       (L) ->
	    Es = bin2term(L, []),
	    {NE, NAcc, NDCT} = output_slots(E, Es, Acc, Head, DCT),
	    output_objs2(NE, NAcc, Head, Cntrs, NDCT, End, 
			 ChunkI-1, MaxNoChunks)
    end.

%% By allocating bigger objects before smaller ones, holes in the
%% buddy system memory map are avoided. Unfortunately, the segments
%% are always allocated first, so if there are objects bigger than a
%% segment, there is a hole to handle. (Haven't considered placing the
%% segments among other objects of the same size.)
allocate_all_objects(Head, Count, Cntrs) ->
    SegSize = actual_seg_size(),
    {Head1, HSz, HN, HA} = alloc_hole(Count, Head, SegSize),
    {Max, _} = hd(Count),
    CT = ?VNEW(Max+1, not_used),
    {Head2, NCT} = allocate_all(Head1, Count, Cntrs, CT),
    Head3 = free_hole(Head2, HSz, HN, HA),
    {Head3, NCT}.

alloc_hole([{LSize,_} | _], Head, SegSz) when ?POW(LSize-1) > SegSz ->
    {_, SegAddr, _} = dets_utils:alloc(Head, SegSz-1),
    Size = ?POW(LSize-1)-1,
    {_, Addr, _} = dets_utils:alloc(Head, Size),
    N = (Addr - SegAddr) div SegSz,
    Head1 = dets_utils:alloc_many(Head, SegSz, N, SegAddr),
    {Head1, SegSz-1, N, SegAddr};
alloc_hole(_Count, Head, _SegSz) ->
    {Head, 0, 0, 0}.

free_hole(Head, _Size, 0, _Addr) ->
    Head;
free_hole(Head, Size, N, Addr) ->
    {Head1, _} = dets_utils:free(Head, Addr, Size),
    free_hole(Head1, Size, N-1, Addr+Size+1).

%% One (temporary) file for each buddy size, write all objects of that
%% size to the file.
allocate_all(Head, [{LSize,NoObjects} | Count], Cntrs, CT) ->
    Size = ?POW(LSize-1)-1,
    {_Head, Addr, _} = dets_utils:alloc(Head, Size),
    NewHead = dets_utils:alloc_many(Head, Size+1, NoObjects, Addr),
    {FileName, Fd} = temp_file(Head, LSize),
    true = ets:insert(Cntrs, {LSize, Addr, {FileName, Fd}, NoObjects}),
    NCT = ?VSET(LSize, CT, [Addr | []]),
    allocate_all(NewHead, Count, Cntrs, NCT);
allocate_all(Head, [], Cntrs, CT) ->
    %% Note that space for the segments has been allocated already.
    %% And one file for the segments...
    {FileName, Fd} = temp_file(Head, ?FSCK_SEGMENT),
    Addr = ?SEGADDR(?SEGARRSZ),
    true = ets:insert(Cntrs, {?FSCK_SEGMENT, Addr, {FileName, Fd}, 0}),
    NCT = ?VSET(tuple_size(CT), CT, [Addr | []]),
    {Head, NCT}.

temp_file(Head, N) ->
    TmpName = lists:concat([Head#head.filename, '.', N]),
    {ok, Fd} = dets_utils:open(TmpName, [raw, binary, write]),
    {TmpName, Fd}.

bin2term([<<Slot:32, LogSize:8, BinTerm/binary>> | BTs], L) ->
    bin2term(BTs, [{Slot, LogSize, BinTerm} | L]);
bin2term([], L) ->
    lists:reverse(L).

write_all_sizes(?DCT(D, CT), Cntrs) ->
    ?DCT(D, write_sizes(1, tuple_size(CT), CT, Cntrs)).

write_sizes(Sz, Sz, CT, Cntrs) ->
    write_size(Sz, ?FSCK_SEGMENT, CT, Cntrs);
write_sizes(Sz, MaxSz, CT, Cntrs) ->
    NCT = write_size(Sz, Sz, CT, Cntrs),
    write_sizes(Sz+1, MaxSz, NCT, Cntrs).

write_size(Sz, I, CT, Cntrs) ->
    case ?VGET(Sz, CT) of
	not_used ->
	    CT;
	[Addr | L] ->
	    {FileName, Fd} = ets:lookup_element(Cntrs, I, 3),
	    case file:write(Fd, lists:reverse(L)) of
		ok ->
		    ?VSET(Sz, CT, [Addr | []]);
		Error ->
		    dets_utils:file_error(FileName, Error)
	    end
    end.

output_slots(E, [E1 | Es], Acc, Head, DCT) 
                       when element(1, E) =:= element(1, E1) ->
    output_slots(E1, Es, [E1 | Acc], Head, DCT);
output_slots(_E, [E | L], Acc, Head, DCT) ->
    NDCT = output_slot(Acc, Head, DCT),
    output_slots(E, L, [E], Head, NDCT);
output_slots(E, [], Acc, _Head, DCT) ->
    {E, Acc, DCT}.

output_slot([E], _Head, ?DCT(D, CT)) ->
    ?DCT(D, output_slot([{foo, E}], 0, foo, CT));
output_slot(Es0, Head, ?DCT(D, CT)) ->
    Kp = Head#head.keypos,
    Fun = fun({_Slot, _LSize, BinTerm} = E) -> 
		  Key = element(Kp, binary_to_term(BinTerm)),
		  {Key, E}
	  end,
    Es = lists:map(Fun, Es0),
    NEs = case Head#head.type of
	      set ->
		  [{Key0,_} = E | L0] = lists:sort(Es),
		  choose_one(lists:sort(L0), Key0, [E]);
	      bag -> 
		  lists:usort(Es);
	      duplicate_bag -> 
		  lists:sort(Es)
	  end,
    Dups = D + length(Es) - length(NEs),
    ?DCT(Dups, output_slot(NEs, 0, foo, CT)).

choose_one([{Key,_} | Es], Key, L) ->
    choose_one(Es, Key, L);
choose_one([{Key,_} = E | Es], _Key, L) ->
    choose_one(Es, Key, [E | L]);
choose_one([], _Key, L) ->
    L.

output_slot([E | Es], Next, _Slot, CT) ->
    {_Key, {Slot, LSize, BinTerm}} = E,
    Size = byte_size(BinTerm),
    Size2 = ?POW(LSize-1),
    Pad = <<0:(Size2-Size-?OHDSZ)/unit:8>>,
    BinObject = [<<Next:32, Size:32, ?ACTIVE:32>>, BinTerm | Pad],
    [Addr | L] = ?VGET(LSize, CT),
    NCT = ?VSET(LSize, CT, [Addr+Size2 | [BinObject | L]]),
    output_slot(Es, Addr, Slot, NCT);
output_slot([], Next, Slot, CT) ->
    I = tuple_size(CT),
    [Addr | L] = ?VGET(I, CT),
    {Pos, _} = slot_position(Slot),
    NoZeros = Pos - Addr,
    BinObject = if 
		    NoZeros > 100 ->
			[dets_utils:make_zeros(NoZeros) | <<Next:32>>];
		    true ->
			<<0:NoZeros/unit:8,Next:32>>
   	        end,
    Size = NoZeros+4,
    ?VSET(I, CT, [Addr+Size | [BinObject | L]]).

%% Does not close Fd.
fsck_input(Head, Fd, Cntrs, _FileHeader) ->
    %% The file is not compressed, so the object size cannot exceed
    %% the filesize, for all objects.
    MaxSz = case file:position(Fd, eof) of
                {ok, Pos} ->
                    Pos;
                _ ->
                    (1 bsl 32) - 1
            end,
    State0 = fsck_read(?BASE, Fd, []),
    fsck_input1(Head, State0, Fd, MaxSz, Cntrs).

fsck_input1(Head, State, Fd, MaxSz, Cntrs) ->
    fun(close) ->
	    ok;
       (read) ->
	    case State of
		done ->
		    end_of_input;
		{done, L} ->
		    R = count_input(Cntrs, L, []),
		    {R, fsck_input1(Head, done, Fd, MaxSz, Cntrs)};
		{cont, L, Bin, Pos} ->
		    R = count_input(Cntrs, L, []),
                    FR = fsck_objs(Bin, Head#head.keypos, Head, []),
		    NewState = fsck_read(FR, Pos, Fd, MaxSz, Head),
		    {R, fsck_input1(Head, NewState, Fd, MaxSz, Cntrs)}
	    end
    end.

%% The ets table Cntrs is used for counting objects per size.
count_input(Cntrs, [[LogSz | B] | Ts], L) ->
    count_object(Cntrs, LogSz),
    count_input(Cntrs, Ts, [B | L]);
count_input(_Cntrs, [], L) ->
    L.

count_object(Cntrs, LogSz) ->
    case catch ets:update_counter(Cntrs, LogSz, 1) of
	N when is_integer(N) -> ok;
	_Badarg -> true = ets:insert(Cntrs, {LogSz, 1})
    end.

fsck_read(Pos, F, L) ->
    case file:position(F, Pos) of
	{ok, _} ->
	    read_more_bytes(<<>>, 0, Pos, F, L);
	_Error ->
	    {done, L}
    end.

fsck_read({more, Bin, Sz, L}, Pos, F, MaxSz, Head) when Sz > MaxSz ->
    FR = skip_bytes(Bin, ?BUMP, Head#head.keypos, Head, L),
    fsck_read(FR, Pos, F, MaxSz, Head);
fsck_read({more, Bin, Sz, L}, Pos, F, _MaxSz, _Head) ->
    read_more_bytes(Bin, Sz, Pos, F, L);
fsck_read({new, Skip, L}, Pos, F, _MaxSz, _Head) ->
    NewPos = Pos + Skip,
    fsck_read(NewPos, F, L).

read_more_bytes(B, Min, Pos, F, L) ->
    Max = if 
	      Min < ?CHUNK_SIZE -> ?CHUNK_SIZE; 
	      true -> Min 
	  end,
    case dets_utils:read_n(F, Max) of
	eof ->
	    {done, L};
	Bin ->
	    NewPos = Pos + byte_size(Bin),
	    {cont, L, list_to_binary([B, Bin]), NewPos}
    end.

fsck_objs(Bin = <<_N:32, Sz:32, Status:32, Tail/binary>>, Kp, Head, L) ->
    if 
	Status =:= ?ACTIVE ->
	    case Tail of
		<<BinTerm:Sz/binary, Tail2/binary>> ->
		    case catch element(Kp, binary_to_term(BinTerm)) of
			{'EXIT', _} ->
			    skip_bytes(Bin, ?BUMP, Kp, Head, L);
			Key ->
			    LogSz = sz2pos(Sz+?OHDSZ),
			    Obj = make_object(Head, Key, LogSz, BinTerm),
			    NL = [[LogSz | Obj] | L],
			    Skip = ?POW(LogSz-1) - Sz - ?OHDSZ,
			    skip_bytes(Tail2, Skip, Kp, Head, NL)
		    end;
		_ ->
                    {more, Bin, Sz, L}
	    end;
	true -> 
	    skip_bytes(Bin, ?BUMP, Kp, Head, L)
    end;
fsck_objs(Bin, _Kp, _Head, L) ->
    {more, Bin, 0, L}.
    
%% Version 8 has to know about version 9.
make_object(Head, Key, _LogSz, BT) when Head#head.version =:= 9 ->
    Slot = dets_v9:db_hash(Key, Head),
    <<Slot:32, BT/binary>>;
make_object(Head, Key, LogSz, BT) ->
    Slot = db_hash(Key, Head),
    <<Slot:32, LogSz:8, BT/binary>>.

%% Inlined.
skip_bytes(Bin, Skip, Kp, Head, L) ->
    case Bin of
	<<_:Skip/binary, Tail/binary>> ->
	    fsck_objs(Tail, Kp, Head, L);
	_ ->
            {new, Skip - byte_size(Bin), L}
    end.

%% -> {NewHead, ok} | throw({Head, Error})
do_perform_save(H) ->
    FL = dets_utils:get_freelists(H),
    B = term_to_binary(FL),
    Size = byte_size(B),
    ?DEBUGF("size of freelist = ~p~n", [Size]),
    ?DEBUGF("head.m = ~p~n", [H#head.m]),
    ?DEBUGF("head.no_objects = ~p~n", [H#head.no_objects]),

    {ok, Pos} = dets_utils:position(H, eof),
    H1 = H#head{freelists_p = Pos},
    W1 = {?FREELIST_POS, <<Pos:32>>},
    W2 = {Pos, [<<0:32, Size:32, ?FREE:32>>, B]},
    
    W3 = {?D_POS, <<(H1#head.m):32, 
	            (H1#head.next):32, 
	            (H1#head.keypos):32,
	            (H1#head.no_objects):32,
		    (H1#head.n):32>>},
    {ClosedProperly, ClosedProperlyNeedCompacitng} = 
	case H1#head.hash_bif of
	    hash ->
		{?CLOSED_PROPERLY2, ?CLOSED_PROPERLY2_NEED_COMPACTING};
	    phash ->
		{?CLOSED_PROPERLY_NEW_HASH, 
		 ?CLOSED_PROPERLY_NEW_HASH_NEED_COMPACTING}
	end,
    W4 = 
	if 
	    Size > 1000, Size > H1#head.no_objects ->
		{?CLOSED_PROPERLY_POS, 
		 <<ClosedProperlyNeedCompacitng:32>>};
	    true ->
		{?CLOSED_PROPERLY_POS, <<ClosedProperly:32>>}
	end,
    W5 = {?FILE_FORMAT_VERSION_POS, <<?FILE_FORMAT_VERSION:32>>},
    {H2, ok} = dets_utils:pwrite(H1, [W1,W2,W3,W4,W5]),
    {ok, Pos2} = dets_utils:position(H2, eof),
    ?DEBUGF("Writing file size ~p, eof at ~p~n", [Pos2+4, Pos2]),
    dets_utils:pwrite(H2, [{Pos2, <<(Pos2 + 4):32>>}]).

%% -> [term()] | throw({Head, Error})
slot_objs(H, Slot) when Slot >= H#head.next ->
    '$end_of_table';
slot_objs(H, Slot) ->
    {_Pos, Chain} = chain(H, Slot),
    collect_chain(H, Chain).

collect_chain(_H, 0) -> [];
collect_chain(H, Pos) ->
    {Next, _Sz, Term} = prterm(H, Pos, ?ReadAhead),
    [Term | collect_chain(H, Next)].

db_hash(Key, Head) ->
    H = h(Key, Head#head.hash_bif),
    Hash = H rem Head#head.m,
    if
	Hash < Head#head.n ->
	    H rem (Head#head.m2); % H rem (2 * m)
	true ->
	    Hash
    end.

h(I, phash) -> erlang:phash(I, ?BIG) - 1;
h(I, HF) -> erlang:HF(I, ?BIG) - 1. %% stupid BIF has 1 counts.

no_slots(_Head) ->
    undefined.

table_parameters(_Head) ->
    undefined.

%% Re-hashing a segment, starting with SlotStart.
%%
%% On the average, half of the objects of the chain are put into a new
%% chain. If the slot of the old chain is i, then the slot of the new
%% chain is i+m.
%% Note that the insertion of objects into the new chain is simplified
%% by the fact that the chains are not sorted on key, which means that
%% each moved object can be inserted first in the new chain.
%% (It is also a fact that the objects with the same key are not sorted.)
%%
%% -> {ok, Writes} | throw({Head, Error})
re_hash(Head, SlotStart) ->
    {SlotPos, _4} = slot_position(SlotStart),
    {ok, Bin} = dets_utils:pread(Head, SlotPos, 4*?SEGSZ, 0),
    {Read, Cs} = split_bin(SlotPos, Bin, [], []),
    re_hash_read(Head, [], Read, Cs).

split_bin(Pos, <<P:32, B/binary>>, R, Cs) ->
    if
	P =:= 0 ->
	    split_bin(Pos+4, B, R, Cs);
	true ->
	    split_bin(Pos+4, B, [{P,?ReadAhead} | R], [[Pos] | Cs])
    end;
split_bin(_Pos, <<>>, R, Cs) ->
    {R, Cs}.

re_hash_read(Head, Cs, R, RCs) ->
    {ok, Bins} = dets_utils:pread(R, Head),
    re_hash_read(Head, R, RCs, Bins, Cs, [], []).

re_hash_read(Head, [{Pos, Size} | Ps], [C | Cs], 
	     [<<Next:32, Sz:32, _Status:32, Bin0/binary>> | Bins], 
	     DoneCs, R, RCs) ->
    case byte_size(Bin0) of
	BinSz when BinSz >= Sz ->
	    case catch binary_to_term(Bin0) of
		{'EXIT', _Error} ->
		    throw(dets_utils:corrupt_reason(Head, bad_object));
		Term ->
		    Key = element(Head#head.keypos, Term),
		    New = h(Key, Head#head.hash_bif) rem Head#head.m2,
		    NC = case New >= Head#head.m of
			     true -> [{Pos,New} | C];
			     false -> [Pos | C]
			 end,
		    if
			Next =:= 0 ->
			    NDoneCs = [NC | DoneCs], 
			    re_hash_read(Head, Ps, Cs, Bins, NDoneCs, R, RCs);
			true ->
			    NR = [{Next,?ReadAhead} | R],
			    NRCs = [NC | RCs],
			    re_hash_read(Head, Ps, Cs, Bins, DoneCs, NR, NRCs)
		    end
	    end;
	BinSz when Size =:= BinSz+?OHDSZ ->
	    NR = [{Pos, Sz+?OHDSZ} | R],
	    re_hash_read(Head, Ps, Cs, Bins, DoneCs, NR, [C | RCs]);
	_BinSz ->
	    throw({Head, {error, {premature_eof, Head#head.filename}}})
    end;
re_hash_read(Head, [], [], [], Cs, [], []) ->
    re_hash_traverse_chains(Cs, Head, [], [], []);
re_hash_read(Head, [], [], [], Cs, R, RCs) ->
    re_hash_read(Head, Cs, R, RCs).

re_hash_traverse_chains([C | Cs], Head, Rs, Ns, Ws) ->
    case re_hash_find_new(C, Rs, start, start) of
	false ->
	    re_hash_traverse_chains(Cs, Head, Rs, Ns, Ws);
	{NRs, FirstNew, LastNew} -> 
	    LastInNew = case C of
			    [{_,_} | _] -> true;
			    _ -> false
			end,
	    N = {FirstNew, LastNew, LastInNew},
	    NWs = re_hash_link(C, start, start, start, Ws),
	    re_hash_traverse_chains(Cs, Head, NRs, [N | Ns], NWs)
    end;
re_hash_traverse_chains([], Head, Rs, Ns, Ws) ->
    {ok, Bins} = dets_utils:pread(Rs, Head),
    {ok, insert_new(Rs, Bins, Ns, Ws)}.

re_hash_find_new([{Pos,NewSlot} | C], R, start, start) ->
    {SPos, _4} = slot_position(NewSlot),
    re_hash_find_new(C, [{SPos,4} | R], Pos, Pos);
re_hash_find_new([{Pos,_SPos} | C], R, _FirstNew, LastNew) ->
    re_hash_find_new(C, R, Pos, LastNew);
re_hash_find_new([_Pos | C], R, FirstNew, LastNew) ->
    re_hash_find_new(C, R, FirstNew, LastNew);
re_hash_find_new([], _R, start, start) ->
    false;
re_hash_find_new([], R, FirstNew, LastNew) ->
    {R, FirstNew, LastNew}.

re_hash_link([{Pos,_SPos} | C], LastOld, start, _LastInNew, Ws) ->
    re_hash_link(C, LastOld, Pos, true, Ws);
re_hash_link([{Pos,_SPos} | C], LastOld, LastNew, false, Ws) ->
    re_hash_link(C, LastOld, Pos, true, [{Pos,<<LastNew:32>>} | Ws]);
re_hash_link([{Pos,_SPos} | C], LastOld, _LastNew, LastInNew, Ws) ->
    re_hash_link(C, LastOld, Pos, LastInNew, Ws);
re_hash_link([Pos | C], start, LastNew, true, Ws) ->
    re_hash_link(C, Pos, LastNew, false, [{Pos,<<0:32>>} | Ws]);
re_hash_link([Pos | C], LastOld, LastNew, true, Ws) ->
    re_hash_link(C, Pos, LastNew, false, [{Pos,<<LastOld:32>>} | Ws]);
re_hash_link([Pos | C], _LastOld, LastNew, LastInNew, Ws) ->
    re_hash_link(C, Pos, LastNew, LastInNew, Ws);
re_hash_link([], _LastOld, _LastNew, _LastInNew, Ws) ->
    Ws.

insert_new([{NewSlotPos,_4} | Rs], [<<P:32>> = PB | Bins], [N | Ns], Ws) ->
    {FirstNew, LastNew, LastInNew} = N,
    Ws1 = case P of
	      0 when LastInNew ->
		  Ws;
	      0 ->
		  [{LastNew, <<0:32>>} | Ws];
	      _ ->
		  [{LastNew, PB} | Ws]
	  end,
    NWs = [{NewSlotPos, <<FirstNew:32>>} | Ws1],
    insert_new(Rs, Bins, Ns, NWs);
insert_new([], [], [], Ws) ->
    Ws.

%% When writing the cache, a 'work list' is first created:
%%   WorkList = [{Key, {Delete,Lookup,[Inserted]}}]
%%   Delete = keep | delete
%%   Lookup = skip | lookup
%%   Inserted = {object(), No}
%%   No = integer()
%% If No =< 0 then there will be -No instances of object() on the file
%% when the cache has been written. If No > 0 then No instances of
%% object() will be added to the file.
%% If Delete has the value 'delete', then all objects with the key Key
%% have been deleted. (This could be viewed as a shorthand for {Object,0}
%% for each object Object on the file not mentioned in some Inserted.)
%% If Lookup has the value 'lookup', all objects with the key Key will
%% be returned.
%%

%% -> {NewHead, [LookedUpObject], pwrite_list()} | throw({NewHead, Error})
write_cache(Head) ->
    #head{cache = C, type = Type} = Head,
    case dets_utils:is_empty_cache(C) of
	true -> {Head, [], []};
	false ->
	    {NewC, _MaxInserts, PerKey} = dets_utils:reset_cache(C),
	    %% NoInsertedKeys is an upper limit on the number of new keys.
	    {WL, NoInsertedKeys} = make_wl(PerKey, Type),
	    Head1 = Head#head{cache = NewC},
	    case may_grow(Head1, NoInsertedKeys, once) of
		{Head2, ok} ->
		    eval_work_list(Head2, WL);
		HeadError ->
		    throw(HeadError)
	    end
    end.

make_wl(PerKey, Type) ->
    make_wl(PerKey, Type, [], 0).

make_wl([{Key,L} | PerKey], Type, WL, Ins) ->
    [Cs | I] = wl(L, Type),
    make_wl(PerKey, Type, [{Key,Cs} | WL], Ins+I);
make_wl([], _Type, WL, Ins) ->
    {WL, Ins}.

wl(L, Type) ->
    wl(L, Type, keep, skip, 0, []).

wl([{_Seq, delete_key} | Cs], Type, _Del, Lookup, _I, _Objs) ->
    wl(Cs, Type, delete, Lookup, 0, []);
wl([{_Seq, {delete_object, Object}} | Cs], Type, Del, Lookup, I, Objs) ->
    NObjs = lists:keydelete(Object, 1, Objs),
    wl(Cs, Type, Del, Lookup, I, [{Object,0} | NObjs]);
wl([{_Seq, {insert, Object}} | Cs], Type, _Del, Lookup, _I, _Objs) 
                    when Type =:= set ->
    wl(Cs, Type, delete, Lookup, 1, [{Object,-1}]);
wl([{_Seq, {insert, Object}} | Cs], Type, Del, Lookup, _I, Objs) ->
    NObjs = 
	case lists:keyfind(Object, 1, Objs) of
	    {_, 0} ->
		lists:keyreplace(Object, 1, Objs, {Object,-1});
	    {_, _C} when Type =:= bag -> % C =:= 1; C =:= -1
		Objs;
	    {_, C} when C < 0 -> % when Type =:= duplicate_bag
		lists:keyreplace(Object, 1, Objs, {Object,C-1});
	    {_, C} -> % when C > 0, Type =:= duplicate_bag
		lists:keyreplace(Object, 1, Objs, {Object,C+1});
	    false when Del =:= delete ->
		[{Object, -1} | Objs];
	    false ->
		[{Object, 1} | Objs]
	end,
    wl(Cs, Type, Del, Lookup, 1, NObjs);
wl([{_Seq, {lookup,_Pid}=Lookup} | Cs], Type, Del, _Lookup, I, Objs) ->
    wl(Cs, Type, Del, Lookup, I, Objs);
wl([], _Type, Del, Lookup, I, Objs) ->
    [{Del, Lookup, Objs} | I].

%% -> {NewHead, ok} | {NewHead, Error}
may_grow(Head, 0, once) ->
    {Head, ok};
may_grow(Head, _N, _How) when Head#head.fixed =/= false ->
    {Head, ok};
may_grow(#head{access = read}=Head, _N, _How) ->
    {Head, ok};
may_grow(Head, _N, _How) when Head#head.next >= ?MAXOBJS ->
    {Head, ok};
may_grow(Head, N, How) ->
    Extra = erlang:min(2*?SEGSZ, Head#head.no_objects + N - Head#head.next),
    case catch may_grow1(Head, Extra, How) of
	{error, Reason} -> % alloc may throw error
	    {Head, {error, Reason}};
	Reply ->
	    Reply
    end.

may_grow1(Head, Extra, many_times) when Extra > ?SEGSZ ->
    Reply = grow(Head, 1, undefined),
    self() ! ?DETS_CALL(self(), may_grow),
    Reply;
may_grow1(Head, Extra, _How) ->    
    grow(Head, Extra, undefined).

%% -> {Head, ok} | throw({Head, Error})
grow(Head, Extra, _SegZero) when Extra =< 0 ->
    {Head, ok};
grow(Head, Extra, undefined) ->
    grow(Head, Extra, seg_zero());
grow(Head, Extra, SegZero) ->
    #head{n = N, next = Next, m = M} = Head,
    SegNum = ?SLOT2SEG(Next),
    {Head0, Ws1} = allocate_segment(Head, SegZero, SegNum),
    {Head1, ok} = dets_utils:pwrite(Head0, Ws1),
    %% If re_hash fails, segp_cache has been called, but it does not matter.
    {ok, Ws2} = re_hash(Head1, N),
    {Head2, ok} = dets_utils:pwrite(Head1, Ws2),
    NewHead =
	if 
	    N + ?SEGSZ =:= M ->
		Head2#head{n = 0, next = Next + ?SEGSZ, m = 2 * M, m2 = 4 * M};
	    true ->
		Head2#head{n = N + ?SEGSZ, next = Next + ?SEGSZ}
	end,
    grow(NewHead, Extra - ?SEGSZ, SegZero).

seg_zero() ->
    <<0:(4*?SEGSZ)/unit:8>>.

find_object(Head, Object) ->
    Key = element(Head#head.keypos, Object),
    Slot = db_hash(Key, Head),
    find_object(Head, Object, Slot).    

find_object(H, _Obj, Slot) when Slot >= H#head.next ->
    false;
find_object(H, Obj, Slot) ->
    {_Pos, Chain} = chain(H, Slot),
    case catch find_obj(H, Obj, Chain) of
	{ok, Pos} ->
	    {ok, Pos};
	_Else ->
	    false
    end.

find_obj(H, Obj, Pos) when Pos > 0 ->
    {Next, _Sz, Term} = prterm(H, Pos, ?ReadAhead),
    if 
	Term == Obj ->
	    {ok, Pos};
	true ->
	    find_obj(H, Obj, Next)
    end.

%% Given, a slot, return the {Pos, Chain} in the file where the
%% objects hashed to this slot reside. Pos is the position in the
%% file where the chain pointer is written and Chain is the position
%% in the file where the first object resides.
chain(Head, Slot) ->
    Pos = ?SEGADDR(?SLOT2SEG(Slot)),
    Segment = get_segp(Pos),
    FinalPos = Segment + (4 * ?REM2(Slot, ?SEGSZ)),
    {ok, <<Chain:32>>} = dets_utils:pread(Head, FinalPos, 4, 0),
    {FinalPos, Chain}.

%%%
%%% Cache routines depending on the dets file format.
%%%

%% -> {Head, [LookedUpObject], pwrite_list()} | throw({Head, Error})
eval_work_list(Head, WorkLists) ->
    SWLs = tag_with_slot(WorkLists, Head, []),
    P1 = dets_utils:family(SWLs), 
    {PerSlot, SlotPositions} = remove_slot_tag(P1, [], []),
    {ok, Bins} = dets_utils:pread(SlotPositions, Head),
    first_object(PerSlot, SlotPositions, Bins, Head, [], [], [], []).

tag_with_slot([{K,_} = WL | WLs], Head, L) ->
    tag_with_slot(WLs, Head, [{db_hash(K, Head), WL} | L]);
tag_with_slot([], _Head, L) ->
    L.

remove_slot_tag([{S,SWLs} | SSWLs], Ls, SPs) ->
    remove_slot_tag(SSWLs, [SWLs | Ls], [slot_position(S) | SPs]);
remove_slot_tag([], Ls, SPs) ->
    {Ls, SPs}.

%% The initial chain pointers and the first object in each chain are
%% read "in parallel", that is, with one call to file:pread/2 (two
%% calls altogether). The following chain objects are read one by
%% one. This is a compromise: if the chains are long and threads are
%% active, it would be faster to keep a state for each chain and read
%% the objects of the chains in parallel, but the overhead would be
%% quite substantial.

first_object([WorkLists | SPs], [{P1,_4} | Ss], [<<P2:32>> | Bs], Head,
	      ObjsToRead, ToRead, Ls, LU) when P2 =:= 0 ->
    L0 = [{old,P1}],
    {L, NLU} = eval_slot(Head, ?ReadAhead, P2, WorkLists, L0, LU),
    first_object(SPs, Ss, Bs, Head, ObjsToRead, ToRead, [L | Ls], NLU);
first_object([WorkLists | SPs], [{P1,_4} | Ss], [<<P2:32>> | Bs], Head, 
	      ObjsToRead, ToRead, Ls, LU) ->
    E = {P1,P2,WorkLists},
    first_object(SPs, Ss, Bs, Head, 
		 [E | ObjsToRead], [{P2, ?ReadAhead} | ToRead], Ls, LU);
first_object([], [], [], Head, ObjsToRead, ToRead, Ls, LU) ->
    {ok, Bins} = dets_utils:pread(ToRead, Head),
    case catch eval_first(Bins, ObjsToRead, Head, Ls, LU) of
	{ok, NLs, NLU} -> 
	    case create_writes(NLs, Head, [], 0) of
		{Head1, [], 0} ->
		    {Head1, NLU, []};
		{Head1, Ws, No} ->
		    {NewHead, Ws2} = update_no_objects(Head1, Ws, No),
		    {NewHead, NLU, Ws2}
	    end;
	_Error -> 
	    throw(dets_utils:corrupt_reason(Head, bad_object))
    end.

%% Update no_objects on the file too, if the number of segments that
%% dets:fsck/6 use for estimate has changed.
update_no_objects(Head, Ws, 0) -> {Head, Ws};
update_no_objects(Head, Ws, Delta) ->
    No = Head#head.no_objects,
    NewNo = No + Delta,
    NWs = 
	if 
	    NewNo > ?MAXOBJS ->
		Ws;
	    ?SLOT2SEG(No) =:= ?SLOT2SEG(NewNo) ->
		Ws;
	    true ->
		[{?NO_OBJECTS_POS, <<NewNo:32>>} | Ws]
	end,
    {Head#head{no_objects = NewNo}, NWs}.

eval_first([<<Next:32, Sz:32, _Status:32, Bin/binary>> | Bins], 
	   [SP | SPs], Head, Ls, LU) ->
    {P1, P2, WLs} = SP,
    L0 = [{old,P1}],
    case byte_size(Bin) of
	BinSz when BinSz >= Sz ->
	    Term = binary_to_term(Bin),
	    Key = element(Head#head.keypos, Term),
	    {L, NLU} = find_key(Head, P2, Next, Sz, Term, Key, WLs, L0, LU),
	    eval_first(Bins, SPs, Head, [L | Ls], NLU);
	_BinSz ->
	    {L, NLU} = eval_slot(Head, Sz+?OHDSZ, P2, WLs, L0, LU),
	    eval_first(Bins, SPs, Head, [L | Ls], NLU)
    end;
eval_first([], [], _Head, Ls, LU) ->
    {ok, Ls, LU}.

eval_slot(_Head, _TrySize, _Pos=0, [], L, LU) ->
    {L, LU};
eval_slot(Head, _TrySize, Pos=0, [WL | WLs], L, LU) ->
    {_Key, {_Delete, LookUp, Objects}} = WL,
    {NL, NLU} = end_of_key(Objects, LookUp, L, []),
    eval_slot(Head, ?ReadAhead, Pos, WLs, NL, NLU++LU);
eval_slot(Head, TrySize, Pos, WLs, L, LU) ->
    {NextPos, Size, Term} = prterm(Head, Pos, TrySize),
    Key = element(Head#head.keypos, Term),
    find_key(Head, Pos, NextPos, Size, Term, Key, WLs, L, LU).

find_key(Head, Pos, NextPos, Size, Term, Key, WLs, L, LU) ->
    case lists:keyfind(Key, 1, WLs) of
	{_, {Delete, LookUp, Objects}} = WL ->
	    NWLs = lists:delete(WL, WLs),
	    {NewObjects, NL, LUK} = eval_object(Size, Term, Delete, LookUp, 
						Objects, Head, Pos, L, []),
	    eval_key(Key, Delete, LookUp, NewObjects, Head, NextPos, 
		     NWLs, NL, LU, LUK);
	false ->
	    L0 = [{old,Pos} | L],
	    eval_slot(Head, ?ReadAhead, NextPos, WLs, L0, LU)
    end.

eval_key(_Key, _Delete, Lookup, _Objects, Head, Pos, WLs, L, LU, LUK) 
                            when Head#head.type =:= set ->
    NLU = case Lookup of
	      {lookup, Pid} -> [{Pid,LUK} | LU];
	      skip -> LU
	  end,
    eval_slot(Head, ?ReadAhead, Pos, WLs, L, NLU);
eval_key(_Key, _Delete, LookUp, Objects, Head, Pos, WLs, L, LU, LUK) 
                                                          when Pos =:= 0 ->
    {NL, NLU} = end_of_key(Objects, LookUp, L, LUK),
    eval_slot(Head, ?ReadAhead, Pos, WLs, NL, NLU++LU);
eval_key(Key, Delete, LookUp, Objects, Head, Pos, WLs, L, LU, LUK) ->
    {NextPos, Size, Term} = prterm(Head, Pos, ?ReadAhead),
    case element(Head#head.keypos, Term) of
	Key ->
	    {NewObjects, NL, LUK1} = 
		eval_object(Size, Term, Delete, LookUp,Objects,Head,Pos,L,LUK),
	    eval_key(Key, Delete, LookUp, NewObjects, Head, NextPos, WLs, 
		     NL, LU, LUK1);
	Key2 ->
	    {L1, NLU} = end_of_key(Objects, LookUp, L, LUK),
	    find_key(Head, Pos, NextPos, Size, Term, Key2, WLs, L1, NLU++LU)
    end.

%% All objects in Objects have the key Key.
eval_object(Size, Term, Delete, LookUp, Objects, Head, Pos, L, LU) ->
    Type = Head#head.type,
    case lists:keyfind(Term, 1, Objects) of
	{_Object, N} when N =:= 0 ->
	    L1 = [{delete,Pos,Size} | L],
	    {Objects, L1, LU};
	{_Object, N} when N < 0, Type =:= set ->
	    L1 = [{old,Pos} | L],
	    wl_lookup(LookUp, Objects, Term, L1, LU);
	{Object, _N} when Type =:= bag -> % when N =:= 1; N =:= -1
	    L1 = [{old,Pos} | L],
	    Objects1 = lists:keydelete(Object, 1, Objects),
	    wl_lookup(LookUp, Objects1, Term, L1, LU);
	{Object, N} when N < 0, Type =:= duplicate_bag ->
	    L1 = [{old,Pos} | L],
	    Objects1 = lists:keyreplace(Object, 1, Objects, {Object,N+1}),
	    wl_lookup(LookUp, Objects1, Term, L1, LU);
	{_Object, N} when N > 0, Type =:= duplicate_bag ->
	    L1 = [{old,Pos} | L],
	    wl_lookup(LookUp, Objects, Term, L1, LU);
	false when Type =:= set, Delete =:= delete ->
	    case lists:keyfind(-1, 2, Objects) of
		false -> % no inserted object, perhaps deleted objects
		    L1 = [{delete,Pos,Size} | L],
		    {[], L1, LU};
		{Term2, -1} ->
		    Bin2 = term_to_binary(Term2),
		    NSize = byte_size(Bin2),
		    Overwrite = 
			if
			    NSize =:= Size ->
				true;
			    true ->
				SizePos = sz2pos(Size+?OHDSZ),
				NSizePos = sz2pos(NSize+?OHDSZ),
				SizePos =:= NSizePos
			end,
		    E = if 
			    Overwrite ->
				{overwrite,Bin2,Pos};
			    true ->
				{replace,Bin2,Pos,Size}
			end,
		    wl_lookup(LookUp, [], Term2, [E | L], LU)
	    end;
	false when Delete =:= delete ->
	    L1 = [{delete,Pos,Size} | L],
	    {Objects, L1, LU};
	false ->
	    L1 = [{old,Pos} | L],
	    wl_lookup(LookUp, Objects, Term, L1, LU)
    end.

%% Inlined.
wl_lookup({lookup,_}, Objects, Term, L, LU) ->
    {Objects, L, [Term | LU]};
wl_lookup(skip, Objects, _Term, L, LU) ->
    {Objects, L, LU}.

end_of_key([{Object,N0} | Objs], LookUp, L, LU) when N0 =/= 0 ->
    N = abs(N0),
    NL = [{insert,N,term_to_binary(Object)} | L],
    NLU = case LookUp of 
	      {lookup, _} ->
		  lists:duplicate(N, Object) ++ LU;
	      skip ->
		  LU
	  end,
    end_of_key(Objs, LookUp, NL, NLU);
end_of_key([_ | Objects], LookUp, L, LU) ->
    end_of_key(Objects, LookUp, L, LU);
end_of_key([], {lookup,Pid}, L, LU) ->
    {L, [{Pid,LU}]};
end_of_key([], skip, L, LU) ->
    {L, LU}.

create_writes([L | Ls], H, Ws, No) ->
    {NH, NWs, NNo} = create_writes(L, H, Ws, No, 0, true),
    create_writes(Ls, NH, NWs, NNo);
create_writes([], H, Ws, No) ->
    {H, lists:reverse(Ws), No}.

create_writes([{old,Pos} | L], H, Ws, No, _Next, true) ->
    create_writes(L, H, Ws, No, Pos, true);
create_writes([{old,Pos} | L], H, Ws, No, Next, false) ->
    W = {Pos, <<Next:32>>},
    create_writes(L, H, [W | Ws], No, Pos, true);
create_writes([{insert,N,Bin} | L], H, Ws, No, Next, _NextIsOld) ->
    {NH, NWs, Pos} = create_inserts(N, H, Ws, Next, byte_size(Bin), Bin),
    create_writes(L, NH, NWs, No+N, Pos, false);
create_writes([{overwrite,Bin,Pos} | L], H, Ws, No, Next, _) ->
    Size = byte_size(Bin),
    W = {Pos, [<<Next:32, Size:32, ?ACTIVE:32>>, Bin]},
    create_writes(L, H, [W | Ws], No, Pos, true);
create_writes([{replace,Bin,Pos,OSize} | L], H, Ws, No, Next, _) ->
    Size = byte_size(Bin),
    {H1, _} = dets_utils:free(H, Pos, OSize+?OHDSZ),
    {NH, NewPos, _} = dets_utils:alloc(H1, ?OHDSZ + Size),
    W1 = {NewPos, [<<Next:32, Size:32, ?ACTIVE:32>>, Bin]},
    NWs = if 
	      Pos =:= NewPos -> 
		  [W1 | Ws];
	      true -> 
		  W2 = {Pos+?STATUS_POS, <<?FREE:32>>},
		  [W1,W2 | Ws]
	  end,
    create_writes(L, NH, NWs, No, NewPos, false);
create_writes([{delete,Pos,Size} | L], H, Ws, No, Next, _) ->
    {NH, _} = dets_utils:free(H, Pos, Size+?OHDSZ),
    NWs = [{Pos+?STATUS_POS,<<?FREE:32>>} | Ws],
    create_writes(L, NH, NWs, No-1, Next, false);
create_writes([], H, Ws, No, _Next, _NextIsOld) ->
    {H, Ws, No}.

create_inserts(0, H, Ws, Next, _Size, _Bin) ->
    {H, Ws, Next};
create_inserts(N, H, Ws, Next, Size, Bin) ->
    {NH, Pos, _} = dets_utils:alloc(H, ?OHDSZ + Size),
    W = {Pos, [<<Next:32, Size:32, ?ACTIVE:32>>, Bin]},
    create_inserts(N-1, NH, [W | Ws], Pos, Size, Bin).

slot_position(S) ->
    Pos = ?SEGADDR(?SLOT2SEG(S)),
    Segment = get_segp(Pos),
    FinalPos = Segment + (4 * ?REM2(S, ?SEGSZ)),
    {FinalPos, 4}.

%% Twice the size of a segment due to the bug in sz2pos/1. Inlined.
actual_seg_size() ->
    ?POW(sz2pos(?SEGSZ*4)-1).

segp_cache(Pos, Segment) ->
    put(Pos, Segment).

%% Inlined.
get_segp(Pos) ->
    get(Pos).

%% Bug: If Sz0 is equal to 2**k for some k, then 2**(k+1) bytes are
%% allocated (wasting 2**k bytes).
sz2pos(N) ->
    1 + dets_utils:log2(N+1).

scan_objs(_Head, Bin, From, To, L, Ts, R, _Type) ->
    scan_objs(Bin, From, To, L, Ts, R).

scan_objs(Bin, From, To, L, Ts, -1) ->
    {stop, Bin, From, To, L, Ts};
scan_objs(B = <<_N:32, Sz:32, St:32, T/binary>>, From, To, L, Ts, R) ->
    if 
	St =:= ?ACTIVE;
	St =:= ?FREE -> % deleted after scanning started
	    case T of
		<<BinTerm:Sz/binary, T2/binary>> ->
		    NTs = [BinTerm | Ts],
		    OSz = Sz + ?OHDSZ,
		    Skip = ?POW(sz2pos(OSz)-1) - OSz,
		    F2 = From + OSz,
		    NR = if 
			     R < 0 ->
				 R + 1;
			     true ->
				 R + OSz + Skip
			 end,
		    scan_skip(T2, F2, To, Skip, L, NTs, NR);
		_ ->
                    {more, From, To, L, Ts, R, Sz+?OHDSZ}
	    end;
	true -> % a segment
	    scan_skip(B, From, To, actual_seg_size(), L, Ts, R)
    end;
scan_objs(_B, From, To, L, Ts, R) ->
    {more, From, To, L, Ts, R, 0}.

scan_skip(Bin, From, To, Skip, L, Ts, R) when From + Skip < To ->
    SkipPos = From + Skip,
    case Bin of
	<<_:Skip/binary, Tail/binary>> ->
	    scan_objs(Tail, SkipPos, To, L, Ts, R);
	_ ->
            {more, SkipPos, To, L, Ts, R, 0}
    end;
scan_skip(Bin, From, To, Skip, L, Ts, R) when From + Skip =:= To ->
    scan_next_allocated(Bin, From, To, L, Ts, R);
scan_skip(_Bin, From, _To, Skip, L, Ts, R) -> % when From + Skip > _To 
    From1 = From + Skip,
    {more, From1, From1, L, Ts, R, 0}.

scan_next_allocated(_Bin, _From, To, <<>>=L, Ts, R) ->
    {more, To, To, L, Ts, R, 0};
scan_next_allocated(Bin, From0, _To, <<From:32, To:32, L/binary>>, Ts, R) ->
    Skip = From - From0,
    scan_skip(Bin, From0, To, Skip, L, Ts, R).

%% Read term from file at position Pos
prterm(Head, Pos, ReadAhead) ->
    Res = dets_utils:pread(Head, Pos, ?OHDSZ, ReadAhead),
    ?DEBUGF("file:pread(~p, ~p, ?) -> ~p~n", [Head#head.filename, Pos, Res]),
    {ok, <<Next:32, Sz:32, _Status:32, Bin0/binary>>} = Res,
    ?DEBUGF("{Next, Sz} = ~p~n", [{Next, Sz}]),
    Bin = case byte_size(Bin0) of
	      Actual when Actual >= Sz ->
		  Bin0;
	      _ ->
		  {ok, Bin1} = dets_utils:pread(Head, Pos +  ?OHDSZ, Sz, 0),
		  Bin1
	  end,
    Term = binary_to_term(Bin),
    {Next, Sz, Term}.

%%%%%%%%%%%%%%%%%  DEBUG functions %%%%%%%%%%%%%%%%

file_info(FH) ->
    #fileheader{closed_properly = CP, keypos = Kp,
                m = M, next = Next, n = N, version = Version,
                type = Type, no_objects = NoObjects} 
        = FH,
    if
        CP =:= 0 ->
            {error, not_closed};
        FH#fileheader.cookie =/= ?MAGIC ->
            {error, not_a_dets_file};
        FH#fileheader.version =/= ?FILE_FORMAT_VERSION ->
            {error, bad_version};
        true ->
            {ok, [{closed_properly,CP},{keypos,Kp},{m, M},
                  {n,N},{next,Next},{no_objects,NoObjects},
                  {type,Type},{version,Version}]}
    end.

v_segments(H) ->
    v_segments(H, 0).

v_segments(_H, ?SEGARRSZ) ->
    done;
v_segments(H, SegNo) ->
    Seg = dets_utils:read_4(H#head.fptr, ?SEGADDR(SegNo)),
    if
	Seg =:= 0 ->
	    done;
	true ->
	    io:format("SEGMENT ~w ", [SegNo]),
	    io:format("At position ~w~n", [Seg]),
	    v_segment(H, SegNo, Seg, 0),
	    v_segments(H, SegNo+1)
    end.

v_segment(_H, _, _SegPos, ?SEGSZ) ->
    done;
v_segment(H, SegNo, SegPos, SegSlot) ->
    Slot = SegSlot + (SegNo * ?SEGSZ),
    Chain = dets_utils:read_4(H#head.fptr, SegPos + (4 * SegSlot)),
    if 
	Chain =:= 0 ->  %% don't print empty chains
	    true;
	true ->
	    io:format("   <~p>~p: [",[SegPos + (4 * SegSlot), Slot]),
	    print_chain(H, Chain)
    end,
    v_segment(H, SegNo, SegPos, SegSlot+1).

print_chain(_H, 0) ->
    io:format("] \n", []);
print_chain(H, Pos) ->
    {ok, _} = file:position(H#head.fptr, Pos),
    case rterm(H#head.fptr) of
	{ok, 0, _Sz, Term} ->
	    io:format("<~p>~p] \n",[Pos, Term]);
	{ok, Next, _Sz, Term} ->
	    io:format("<~p>~p, ", [Pos, Term]),
	    print_chain(H, Next);
	Other ->
	    io:format("~nERROR ~p~n", [Other])
    end.

%% Can't be used at the bucket level!!!!
%% Only when we go down a chain
rterm(F) ->
    case catch rterm2(F) of
	{'EXIT', Reason} -> %% truncated DAT file 
	    dets_utils:vformat("** dets: Corrupt or truncated dets file~n", 
                               []), 
	    {error, Reason};
	Other -> 
	    Other
    end.

rterm2(F) ->
    {ok, <<Next:32, Sz:32, _:32>>} = file:read(F, ?OHDSZ),
    {ok, Bin} = file:read(F, Sz),
    Term = binary_to_term(Bin),
    {ok, Next, Sz, Term}.