262 lines
8.3 KiB
Erlang
262 lines
8.3 KiB
Erlang
%%
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%% This module provides functions for managing bst files - a modified version
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%% of sst files, to be used in leveleddb.
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%% bst files are broken into the following sections:
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%% - Header (fixed width 32 bytes - containing pointers and metadata)
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%% - Blocks (variable length)
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%% - Slots (variable length)
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%% - Footer (variable length - contains slot index and helper metadata)
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%%
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%% The 32-byte header is made up of
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%% - 1 byte version (major 5 bits, minor 3 bits) - default 0.1
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%% - 1 byte state bits (1 bit to indicate mutability, 1 for use of compression)
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%% - 4 bytes footer position
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%% - 4 bytes slot list length
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%% - 4 bytes helper length
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%% - 14 bytes spare for future options
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%% - 4 bytes CRC (header)
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%%
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%% A key in the file is a tuple of {Key, Value/Metadata, Sequence #, State}
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%% - Keys are themselves tuples, and all entries must be added to the bst
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%% in key order
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%% - Metadata can be null or some fast-access information that may be required
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%% in preference to the full value (e.g. vector clocks, hashes). This could
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%% be a value instead of Metadata should the file be sued in an alternate
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%% - Sequence numbers is the integer representing the order which the item
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%% was added (which also acts as reference to find the cdb file under which
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%% the value is stored)
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%% - State can be tomb (for tombstone), active or {timestamp, TS}
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%%
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%% The Blocks is a series of blocks of:
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%% - 4 byte block length
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%% - variable-length compressed list of 32 keys & values
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%% - 4 byte CRC for block
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%% There will be up to 4000 blocks in a single bst file
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%%
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%% The slots is a series of references
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%% - 4 byte bloom-filter length
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%% - 4 byte key-helper length
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%% - a variable-length compressed bloom filter for all keys in slot (approx 3KB)
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%% - 64 ordered variable-length key helpers pointing to first key in each
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%% block (in slot) of the form Key Length, Key, Block Position
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%% - 4 byte CRC for the slot
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%% - ulitmately a slot covers 64 x 32 = 2048 keys
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%%
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%% The slot index in the footer is made up of 64 keys and pointers at the
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%% the start of each slot
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%% - 64 x Key Length (4 byte), Key, Position (4 byte) indexes
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%% - 4 bytes CRC for the index
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%%
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%% The format of the file is intended to support quick lookups, whilst
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%% allowing for a new file to be written incrementally (so that all keys and
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%% values need not be retained in memory) - perhaps n blocks at a time
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-module(leveled_bst).
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-export([start_file/1, convert_header/1, append_slot/4]).
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-include_lib("eunit/include/eunit.hrl").
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-define(WORD_SIZE, 4).
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-define(CURRENT_VERSION, {0,1}).
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-define(SLOT_COUNT, 64).
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-define(BLOCK_SIZE, 32).
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-define(SLOT_SIZE, 64).
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-record(metadata, {version = ?CURRENT_VERSION :: tuple(),
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mutable = false :: true | false,
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compressed = true :: true | false,
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slot_index,
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open_slot :: integer(),
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cache :: tuple(),
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smallest_key :: tuple(),
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largest_key :: tuple(),
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smallest_sqn :: integer(),
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largest_sqn :: integer()
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}).
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-record(object, {key :: tuple(),
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value,
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sequence_numb :: integer(),
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state}).
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%% Start a bare file with an initial header and no further details
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%% Return the {Handle, metadata record}
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start_file(FileName) when is_list(FileName) ->
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{ok, Handle} = file:open(FileName, [binary, raw, read, write]),
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start_file(Handle);
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start_file(Handle) ->
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Header = create_header(initial),
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{ok, _} = file:position(Handle, bof),
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ok = file:write(Handle, Header),
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{Version, {M, C}, _, _} = convert_header(Header),
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FileMD = #metadata{version = Version, mutable = M, compressed = C,
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slot_index = array:new(?SLOT_COUNT), open_slot = 0},
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{Handle, FileMD}.
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create_header(initial) ->
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{Major, Minor} = ?CURRENT_VERSION,
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Version = <<Major:5, Minor:3>>,
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State = <<0:6, 1:1, 1:1>>, % Mutable and compressed
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Lengths = <<0:32, 0:32, 0:32>>,
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Options = <<0:112>>,
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H1 = <<Version/binary, State/binary, Lengths/binary, Options/binary>>,
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CRC32 = erlang:crc32(H1),
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<<H1/binary, CRC32:32/integer>>.
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convert_header(Header) ->
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<<H1:28/binary, CRC32:32/integer>> = Header,
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case erlang:crc32(H1) of
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CRC32 ->
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<<Major:5/integer, Minor:3/integer, _/binary>> = H1,
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case {Major, Minor} of
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{0, 1} ->
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convert_header_v01(H1);
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_ ->
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unknown_version
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end;
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_ ->
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crc_mismatch
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end.
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convert_header_v01(Header) ->
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<<_:8, 0:6, Mutable:1, Comp:1,
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FooterP:32/integer, SlotLng:32/integer, HlpLng:32/integer,
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_/binary>> = Header,
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case Mutable of
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1 -> M = true;
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0 -> M = false
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end,
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case Comp of
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1 -> C = true;
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0 -> C = false
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end,
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{{0, 1}, {M, C}, {FooterP, SlotLng, HlpLng}, none}.
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%% Append a slot of blocks to the end file, and update the slot index in the
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%% file metadata
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append_slot(Handle, SortedKVList, SlotCount, FileMD) ->
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{ok, _} = file:position(Handle, eof),
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{KeyList, BlockIndexBin, BlockBin} = add_blocks(SortedKVList),
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ok = file:write(Handle, BlockBin),
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[TopObject|_] = SortedKVList,
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BloomBin = leveled_rice:create_bloom(KeyList),
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SlotIndex = array:set(SlotCount,
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{TopObject#object.key, BloomBin, BlockIndexBin},
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FileMD#metadata.slot_index),
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{Handle, FileMD#metadata{slot_index=SlotIndex}}.
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add_blocks(SortedKVList) ->
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add_blocks(SortedKVList, [], [], [], 0).
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add_blocks([], KeyList, BlockIndex, BlockBinList, _) ->
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{KeyList, serialise_blockindex(BlockIndex), list_to_binary(BlockBinList)};
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add_blocks(SortedKVList, KeyList, BlockIndex, BlockBinList, Position) ->
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case length(SortedKVList) of
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KeyCount when KeyCount >= ?BLOCK_SIZE ->
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{TopBlock, Rest} = lists:split(?BLOCK_SIZE, SortedKVList);
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KeyCount ->
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{TopBlock, Rest} = lists:split(KeyCount, SortedKVList)
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end,
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[TopKey|_] = TopBlock,
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TopBin = serialise_block(TopBlock),
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add_blocks(Rest, add_to_keylist(KeyList, TopBlock),
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[{TopKey, Position}|BlockIndex],
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[TopBin|BlockBinList], Position + byte_size(TopBin)).
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add_to_keylist(KeyList, []) ->
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KeyList;
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add_to_keylist(KeyList, [TopKV|Rest]) ->
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add_to_keylist([map_keyforbloom(TopKV)|KeyList], Rest).
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map_keyforbloom(_Object=#object{key=Key}) ->
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Key.
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serialise_blockindex(BlockIndex) ->
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serialise_blockindex(BlockIndex, <<>>).
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serialise_blockindex([], BlockBin) ->
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BlockBin;
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serialise_blockindex([TopIndex|Rest], BlockBin) ->
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{Key, BlockPos} = TopIndex,
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KeyBin = serialise_key(Key),
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KeyLength = byte_size(KeyBin),
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serialise_blockindex(Rest,
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<<KeyLength:32/integer, KeyBin/binary, BlockPos:32/integer,
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BlockBin/binary>>).
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serialise_block(Block) ->
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term_to_binary(Block).
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serialise_key(Key) ->
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term_to_binary(Key).
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%%%%%%%%%%%%%%%%
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% T E S T
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%%%%%%%%%%%%%%%
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create_sample_kv(Prefix, Counter) ->
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Key = {o, "Bucket1", lists:concat([Prefix, Counter])},
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Object = #object{key=Key, value=null,
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sequence_numb=random:uniform(1000000), state=active},
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Object.
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create_ordered_kvlist(KeyList, 0) ->
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KeyList;
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create_ordered_kvlist(KeyList, Length) ->
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KV = create_sample_kv("Key", Length),
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create_ordered_kvlist([KV|KeyList], Length - 1).
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empty_header_test() ->
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Header = create_header(initial),
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?assertMatch(32, byte_size(Header)),
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<<Major:5, Minor:3, _/binary>> = Header,
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?assertMatch({0, 1}, {Major, Minor}),
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{Version, State, Lengths, Options} = convert_header(Header),
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?assertMatch({0, 1}, Version),
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?assertMatch({true, true}, State),
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?assertMatch({0, 0, 0}, Lengths),
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?assertMatch(none, Options).
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bad_header_test() ->
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Header = create_header(initial),
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<<_:1/binary, Rest/binary >> = Header,
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HdrDetails1 = convert_header(<<0:5/integer, 2:3/integer, Rest/binary>>),
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?assertMatch(crc_mismatch, HdrDetails1),
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<<_:1/binary, RestToCRC:27/binary, _:32/integer>> = Header,
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NewHdr1 = <<0:5/integer, 2:3/integer, RestToCRC/binary>>,
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CRC32 = erlang:crc32(NewHdr1),
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NewHdr2 = <<NewHdr1/binary, CRC32:32/integer>>,
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?assertMatch(unknown_version, convert_header(NewHdr2)).
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record_onstartfile_test() ->
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{_, FileMD} = start_file("onstartfile.bst"),
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?assertMatch({0, 1}, FileMD#metadata.version),
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ok = file:delete("onstartfile.bst").
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append_initialblock_test() ->
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{Handle, FileMD} = start_file("onstartfile.bst"),
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KVList = create_ordered_kvlist([], 2048),
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Key1 = {o, "Bucket1", "Key1"},
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[TopObj|_] = KVList,
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?assertMatch(Key1, TopObj#object.key),
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{_, UpdFileMD} = append_slot(Handle, KVList, 0, FileMD),
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{TopKey1, BloomBin, _} = array:get(0, UpdFileMD#metadata.slot_index),
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io:format("top key of ~w~n", [TopKey1]),
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?assertMatch(Key1, TopKey1),
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?assertMatch(true, leveled_rice:check_key(Key1, BloomBin)),
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?assertMatch(false, leveled_rice:check_key("OtherKey", BloomBin)).
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