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Add reverse iteration to btree iterator
+89
-8
+3
-3
lib/btree/fuzz/model_fuzz.ex
+3
-3
lib/btree/fuzz/model_fuzz.ex
···
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start_key = make_key(opt_key_bits)
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count = Enum.random(1..10)
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reverse? = false
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#dbg {start_key, count}
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reverse? = Enum.random([true, false])
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#dbg {start_key, count, reverse?}
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#dbg SimpleKV.dump(simple_kv), limit: :infinity
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btree_pairs = scan(btree, start_key, count, reverse?)
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skv_pairs = SimpleKV.scan(simple_kv, start_key, count)
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skv_pairs = SimpleKV.scan(simple_kv, start_key, count, reverse?)
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assert btree_pairs == skv_pairs
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state
+10
-3
lib/btree/fuzz/simple_kv.ex
+10
-3
lib/btree/fuzz/simple_kv.ex
···
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end)
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end
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@spec scan(t, binary, non_neg_integer) :: [{binary, binary}]
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def scan(simple_kv, start_key, count) do
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@spec scan(t, binary, non_neg_integer, boolean) :: [{binary, binary}]
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def scan(simple_kv, start_key, count, _reverse? = true) do
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simple_kv
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|> Enum.sort_by(fn {k, _v} -> k end, :desc)
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|> Enum.filter(fn {k, _v} -> k < start_key end)
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|> Enum.take(count)
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end
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def scan(simple_kv, start_key, count, _reverse? = false) do
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simple_kv
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|> Enum.sort_by(fn {k, _v} -> k end)
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|> Enum.sort_by(fn {k, _v} -> k end, :asc)
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|> Enum.filter(fn {k, _v} -> k >= start_key end)
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|> Enum.take(count)
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end
+76
-2
lib/btree/iterator.ex
+76
-2
lib/btree/iterator.ex
···
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[{:root_address, {root_index, root_checksum}}] = :ets.lookup(root_store, :root_address)
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root_data = BTree.read_page(page_store, root_index, root_checksum)
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iterator = %Iterator{
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it = %Iterator{
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btree: btree,
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page_stack: [],
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current_page: root_data,
···
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current_pair: nil,
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reverse?: reverse?,
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}
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seek_forward(iterator, start_key)
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case reverse? do
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true -> seek_backward(it, start_key)
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false -> seek_forward(it, start_key)
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end
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end
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@spec next(t) :: t
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def next(%Iterator{reverse?: false} = it), do: next_forward(it)
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def next(%Iterator{reverse?: true} = it), do: next_backward(it)
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defp seek_backward(%Iterator{} = it, search_key) do
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it = seek(it, search_key)
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{key, _value} = it.current_pair
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case key >= search_key do
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true -> next_backward(it)
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false -> it
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end
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end
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defp seek_forward(%Iterator{} = it, search_key) do
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it = seek(it, search_key)
···
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case (key >= search_key) or (i == (pair_count - 1)) do
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true -> {i, {key, value}}
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false -> do_seek_leaf(page_data, slots_start, pair_count, search_key, i + 1)
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end
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end
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defp next_backward(%Iterator{} = it) do
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%{
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current_page: current_page,
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current_i: current_i,
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} = it
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<<
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_::binary-size(byte_size(current_page) - c_page_trailer_bytes()),
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# TODO: cache these in the iterator
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pair_count::integer-16,
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type_byte::integer-8,
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>> = current_page
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case current_i > 0 do
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true ->
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current_i = current_i - 1
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case type_byte do
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0x00 ->
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child_page = inner_child_page_at(it.btree.page_store, current_page, pair_count, current_i)
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<<
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_::binary-size(byte_size(current_page) - c_page_trailer_bytes()),
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child_pair_count::integer-16,
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_type_byte::integer-8,
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>> = current_page
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it = %{it |
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page_stack: [{current_i, current_page} | it.page_stack],
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current_page: child_page,
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current_i: child_pair_count,
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current_pair: nil,
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}
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next_forward(it)
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0x01 ->
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current_pair = leaf_pair_at(current_page, pair_count, current_i)
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%{it |
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current_i: current_i,
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current_pair: current_pair,
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}
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end
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false ->
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case it.page_stack do
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[] ->
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%{it |
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current_pair: :infinity,
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}
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[{page, i} | stack_rest] ->
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it = %{it |
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page_stack: stack_rest,
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current_page: page,
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current_i: i,
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}
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next_forward(it)
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end
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end
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end
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