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Update comments to assist with clarity

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This commit is contained in:
Martin Sumner 2018-11-15 08:54:06 +00:00
parent a12931b430
commit fab11bc2d2
1 changed files with 29 additions and 5 deletions
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34
src/leveled_sst.erl
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@ -1710,6 +1710,8 @@ read_slots(Handle, SlotList, {SegList, LowLastMod, BlockIndexCache},
% Need to find just the right keys
PositionList =
find_pos(BlockIdx, SegList, [], 0),
% Note check_blocks should return [] if
% PositionList is empty (which it may be)
KVL =
check_blocks(PositionList,
{Handle, SP},
@ -1720,13 +1722,11 @@ read_slots(Handle, SlotList, {SegList, LowLastMod, BlockIndexCache},
IdxModDate,
[]),
% There is no range passed through to the
% binaryslot_reader, so this needs to
% filtered
% binaryslot_reader, so these results need
% to be filtered
FilterFun =
fun(KV) -> in_range(KV, SK, EK) end,
Acc ++ lists:filter(FilterFun, KVL)
% Note check_blocks shouldreturn [] if
% PositionList is empty
end
end
end
@ -1760,8 +1760,25 @@ read_slotlist(SlotList, Handle) ->
list({integer(), binary()})}.
%% @doc
%% Read the binary slots converting them to {K, V} pairs if they were not
%% already {K, V} pairs
%% already {K, V} pairs. If they are already {K, V} pairs it is assumed
%% that they have already been range checked before extraction.
%%
%% Keys which are still to be extracted from the slot, are accompanied at
%% this function by the range against which the keys need to be checked.
%% This range is passed with the slot to binaryslot_trimmedlist which should
%% open the slot block by block, filtering individual keys where the endpoints
%% of the block are outside of the range, and leaving blocks already proven to
%% be outside of the range unopened.
binaryslot_reader(SlotBinsToFetch, PressMethod, IdxModDate, SegList) ->
% Two accumulators are added.
% One to collect the list of keys and values found in the binary slots
% (subject to range filtering if the slot is still deserialised at this
% stage.
% The second accumulator extracts the header information from the slot, so
% that the cache can be built for that slot. This is used by the handling
% of get_kvreader calls. This means that slots which are only used in
% range queries can still populate their block_index caches (on the FSM
% loop state), and those caches can be used for future queries.
binaryslot_reader(SlotBinsToFetch,
PressMethod, IdxModDate, SegList, [], []).
@ -1769,6 +1786,11 @@ binaryslot_reader([], _PressMethod, _IdxModDate, _SegList, Acc, BIAcc) ->
{Acc, BIAcc};
binaryslot_reader([{SlotBin, ID, SK, EK}|Tail],
PressMethod, IdxModDate, SegList, Acc, BIAcc) ->
% The start key and end key here, may not the start key and end key the
% application passed into the query. If the slot is known to lie entirely
% inside the range, on either of both sides, the SK and EK may be
% substituted for the 'all' key work to indicate there is no need for
% entries in this slot to be trimmed from either or both sides.
{TrimmedL, BICache} =
binaryslot_trimmedlist(SlotBin,
SK, EK,
@ -1783,6 +1805,8 @@ binaryslot_reader([{SlotBin, ID, SK, EK}|Tail],
[{ID, BICache}|BIAcc]);
binaryslot_reader([{K, V}|Tail],
PressMethod, IdxModDate, SegList, Acc, BIAcc) ->
% These entries must already have been filtered for membership inside any
% range used in the query.
binaryslot_reader(Tail,
PressMethod, IdxModDate, SegList,
Acc ++ [{K, V}], BIAcc).