Use more keys in bloom
Use 4 keys in the bloom (which is closer to optimal size). This should halve the fpr - as we cna now use the large ExtraHash rather than being constrained by the SegmentHash here.
This commit is contained in:
Martin Sumner
parent
f08faf6432
commit
6af1d3b003
2 changed files with 31 additions and 86 deletions
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@ -88,7 +88,7 @@
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%% speed can be gained if just the segment ID is known - but more can be
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%% gained should the extended hash (with the second element) is known
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segment_hash(Key) when is_binary(Key) ->
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<<SegmentID:16/integer, ExtraHash:16/integer, _Rest/binary>> =
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<<SegmentID:16/integer, ExtraHash:32/integer, _Rest/binary>> =
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crypto:hash(md5, Key),
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{SegmentID, ExtraHash};
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segment_hash(Key) ->
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@ -16,8 +16,8 @@
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check_hash/2
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]).
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-define(BITS_PER_KEY, 8). % Must be 8 or 4
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-define(INTEGER_SIZE, ?BITS_PER_KEY * 8).
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-define(BLOOM_SIZE_BYTES, 16).
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-define(INTEGER_SIZE, 128).
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-define(BAND_MASK, ?INTEGER_SIZE - 1).
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@ -34,9 +34,8 @@ create_bloom(HashList) ->
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<<>>;
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L when L > 32 ->
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add_hashlist(HashList,
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15,
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0);
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7,
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0, 0, 0, 0, 0, 0, 0, 0);
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L when L > 16 ->
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add_hashlist(HashList, 3, 0, 0, 0, 0);
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_ ->
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@ -49,10 +48,10 @@ create_bloom(HashList) ->
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check_hash(_Hash, <<>>) ->
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false;
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check_hash({_SegHash, Hash}, BloomBin) ->
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SlotSplit = (byte_size(BloomBin) div ?BITS_PER_KEY) - 1,
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{Slot, H0, H1, H2, H3} = split_hash(Hash, SlotSplit),
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Mask = get_mask(H0, H1, H2, H3),
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Pos = Slot * ?BITS_PER_KEY,
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SlotSplit = (byte_size(BloomBin) div ?BLOOM_SIZE_BYTES) - 1,
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{Slot, Hashes} = split_hash(Hash, SlotSplit),
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Mask = get_mask(Hashes),
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Pos = Slot * ?BLOOM_SIZE_BYTES,
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IntSize = ?INTEGER_SIZE,
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<<_H:Pos/binary, CheckInt:IntSize/integer, _T/binary>> = BloomBin,
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case CheckInt band Mask of
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@ -69,12 +68,12 @@ check_hash({_SegHash, Hash}, BloomBin) ->
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split_hash(Hash, SlotSplit) ->
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Slot = Hash band SlotSplit,
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H0 = (Hash bsr 4) band (?BAND_MASK),
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H1 = (Hash bsr 10) band (?BAND_MASK),
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H2 = (Hash bsr 16) band (?BAND_MASK),
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H3 = (Hash bsr 24) band (?BAND_MASK),
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{Slot, H0, H1, H2, H3}.
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H1 = (Hash bsr 11) band (?BAND_MASK),
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H2 = (Hash bsr 18) band (?BAND_MASK),
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H3 = (Hash bsr 25) band (?BAND_MASK),
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{Slot, [H0, H1, H2, H3]}.
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get_mask(H0, H1, H2, H3) ->
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get_mask([H0, H1, H2, H3]) ->
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(1 bsl H0) bor (1 bsl H1) bor (1 bsl H2) bor (1 bsl H3).
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@ -85,8 +84,8 @@ add_hashlist([], _S, S0, S1) ->
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IntSize = ?INTEGER_SIZE,
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<<S0:IntSize/integer, S1:IntSize/integer>>;
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add_hashlist([{_SegHash, TopHash}|T], SlotSplit, S0, S1) ->
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{Slot, H0, H1, H2, H3} = split_hash(TopHash, SlotSplit),
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Mask = get_mask(H0, H1, H2, H3),
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{Slot, Hashes} = split_hash(TopHash, SlotSplit),
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Mask = get_mask(Hashes),
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case Slot of
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0 ->
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add_hashlist(T, SlotSplit, S0 bor Mask, S1);
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@ -99,8 +98,8 @@ add_hashlist([], _S, S0, S1, S2, S3) ->
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<<S0:IntSize/integer, S1:IntSize/integer,
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S2:IntSize/integer, S3:IntSize/integer>>;
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add_hashlist([{_SegHash, TopHash}|T], SlotSplit, S0, S1, S2, S3) ->
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{Slot, H0, H1, H2, H3} = split_hash(TopHash, SlotSplit),
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Mask = get_mask(H0, H1, H2, H3),
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{Slot, Hashes} = split_hash(TopHash, SlotSplit),
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Mask = get_mask(Hashes),
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case Slot of
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0 ->
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add_hashlist(T, SlotSplit, S0 bor Mask, S1, S2, S3);
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@ -112,104 +111,50 @@ add_hashlist([{_SegHash, TopHash}|T], SlotSplit, S0, S1, S2, S3) ->
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add_hashlist(T, SlotSplit, S0, S1, S2, S3 bor Mask)
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end.
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add_hashlist([], _S, S0, S1, S2, S3, S4, S5, S6, S7, S8, S9,
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SA, SB, SC, SD, SE, SF) ->
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add_hashlist([], _S, S0, S1, S2, S3, S4, S5, S6, S7) ->
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IntSize = ?INTEGER_SIZE,
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<<S0:IntSize/integer, S1:IntSize/integer,
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S2:IntSize/integer, S3:IntSize/integer,
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S4:IntSize/integer, S5:IntSize/integer,
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S6:IntSize/integer, S7:IntSize/integer,
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S8:IntSize/integer, S9:IntSize/integer,
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SA:IntSize/integer, SB:IntSize/integer,
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SC:IntSize/integer, SD:IntSize/integer,
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SE:IntSize/integer, SF:IntSize/integer>>;
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S6:IntSize/integer, S7:IntSize/integer>>;
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add_hashlist([{_SegHash, TopHash}|T],
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7, S8, S9,
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SA, SB, SC, SD, SE, SF) ->
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{Slot, H0, H1, H2, H3} = split_hash(TopHash, SlotSplit),
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Mask = get_mask(H0, H1, H2, H3),
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S0, S1, S2, S3, S4, S5, S6, S7) ->
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{Slot, Hashes} = split_hash(TopHash, SlotSplit),
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Mask = get_mask(Hashes),
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case Slot of
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0 ->
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add_hashlist(T,
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SlotSplit,
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S0 bor Mask, S1, S2, S3, S4, S5, S6, S7, S8, S9,
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SA, SB, SC, SD, SE, SF);
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S0 bor Mask, S1, S2, S3, S4, S5, S6, S7);
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1 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1 bor Mask, S2, S3, S4, S5, S6, S7, S8, S9,
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SA, SB, SC, SD, SE, SF);
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S0, S1 bor Mask, S2, S3, S4, S5, S6, S7);
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2 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2 bor Mask, S3, S4, S5, S6, S7, S8, S9,
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SA, SB, SC, SD, SE, SF);
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S0, S1, S2 bor Mask, S3, S4, S5, S6, S7);
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3 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3 bor Mask, S4, S5, S6, S7, S8, S9,
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SA, SB, SC, SD, SE, SF);
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S0, S1, S2, S3 bor Mask, S4, S5, S6, S7);
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4 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4 bor Mask, S5, S6, S7, S8, S9,
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SA, SB, SC, SD, SE, SF);
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S0, S1, S2, S3, S4 bor Mask, S5, S6, S7);
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5 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5 bor Mask, S6, S7, S8, S9,
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SA, SB, SC, SD, SE, SF);
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S0, S1, S2, S3, S4, S5 bor Mask, S6, S7);
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6 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6 bor Mask, S7, S8, S9,
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SA, SB, SC, SD, SE, SF);
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S0, S1, S2, S3, S4, S5, S6 bor Mask, S7);
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7 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7 bor Mask, S8, S9,
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SA, SB, SC, SD, SE, SF);
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8 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7, S8 bor Mask, S9,
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SA, SB, SC, SD, SE, SF);
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9 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7, S8, S9 bor Mask,
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SA, SB, SC, SD, SE, SF);
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10 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7, S8, S9,
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SA bor Mask, SB, SC, SD, SE, SF);
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11 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7, S8, S9,
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SA, SB bor Mask, SC, SD, SE, SF);
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12 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7, S8, S9,
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SA, SB, SC bor Mask, SD, SE, SF);
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13 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7, S8, S9,
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SA, SB, SC, SD bor Mask, SE, SF);
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14 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7, S8, S9,
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SA, SB, SC, SD, SE bor Mask, SF);
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15 ->
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add_hashlist(T,
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SlotSplit,
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S0, S1, S2, S3, S4, S5, S6, S7, S8, S9,
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SA, SB, SC, SD, SE, SF bor Mask)
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S0, S1, S2, S3, S4, S5, S6, S7 bor Mask)
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end.
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