defmodule Datadog.Sketch.Store.Dense do
@moduledoc """
The Dense store is a dynamically growing contiguous (non-sparse) store. The
number of bins are bound only by the size of the `:array` that can be allocated.
"""
@behaviour Datadog.Sketch.Store
alias Datadog.Sketch.Store
@array_length_overhead 64
@array_length_growth_increment 0.1
defstruct bins: :array.new(0, [{:fixed, true}, {:default, 0}]),
count: 0.0,
offset: 0,
# Max 32, bit integer Erlang supports. Forces a resize when adding
# the first number.
min_index: 134_217_728,
max_index: -134_217_729
@type t :: %__MODULE__{
bins: :array.array(),
count: float(),
offset: integer(),
min_index: integer(),
max_index: integer()
}
@doc """
Creates a new dense store.
## Examples
iex> Dense.new()
%Dense{}
"""
@spec new :: t()
def new do
%__MODULE__{}
end
@doc """
Adds a number to the store.
## Examples
iex> %Dense{} = Dense.add(Dense.new(), 100)
"""
@impl Datadog.Sketch.Store
@spec add(t(), integer()) :: t()
def add(store, index) do
add_with_count(store, index, 1.0)
end
@doc """
Adds a bin type to the store.
## Examples
iex> %Dense{} = Dense.add_bin(Dense.new(), %{index: 100, count: 13.13})
"""
@impl Datadog.Sketch.Store
@spec add_bin(t(), Store.bin()) :: t()
def add_bin(store, %{count: 0.0}), do: store
def add_bin(store, %{count: count, index: index}) do
add_with_count(store, index, count)
end
@doc """
Adds multiple bin types to the store.
## Examples
iex> %Dense{} = Dense.add_bins(Dense.new(), [
...> %{index: 100, count: 13.13},
...> %{index: 20, count: 2342.4}
...> ])
"""
@impl Datadog.Sketch.Store
@spec add_bins(t(), [Store.bin()]) :: t()
def add_bins(store, bins) when is_list(bins),
do: Enum.reduce(bins, store, &add_bin(&2, &1))
@doc """
Adds a number to the store `count` number of times.
## Examples
iex> %Dense{} = Dense.add_with_count(Dense.new(), 100, 13.13)
iex> %Dense{} = Dense.add_with_count(Dense.new(), 987, 8.3e12)
"""
@impl Datadog.Sketch.Store
@spec add_with_count(t(), integer(), float()) :: t()
def add_with_count(store, _index, 0), do: store
def add_with_count(store, index, count) do
{store, array_index} = normalize(store, index)
current_value = safe_get(store.bins, array_index)
new_bins = :array.set(array_index, current_value + count, store.bins)
%{store | bins: new_bins, count: store.count + count}
end
@spec safe_get(:array.array(), integer()) :: integer()
defp safe_get(array, index) do
:array.get(index, array)
rescue
ArgumentError -> 0
end
@spec normalize(t(), integer()) :: {t(), integer()}
defp normalize(store, index) do
if index < store.min_index or index > store.max_index do
store = extend_range(store, index, index)
{store, index - store.offset}
else
{store, index - store.offset}
end
end
@spec get_new_length(integer(), integer()) :: integer()
defp get_new_length(new_min_index, new_max_index) do
desired_length = new_max_index - new_min_index + 1
round(
((desired_length + @array_length_overhead - 1) / @array_length_growth_increment + 1) *
@array_length_growth_increment
)
end
@spec extend_range(t(), integer(), integer()) :: t()
defp extend_range(store, new_min_index, new_max_index) do
new_min_index = min(new_min_index, store.min_index)
new_max_index = max(new_max_index, store.max_index)
cond do
empty?(store) ->
initial_length = get_new_length(new_min_index, new_max_index)
store = %{
store
| bins: :array.new(initial_length, [{:fixed, true}, {:default, 0}]),
offset: new_min_index,
min_index: new_min_index,
max_index: new_max_index
}
adjust(store, new_min_index, new_max_index)
new_min_index >= store.offset and new_max_index < store.offset + :array.size(store.bins) ->
%{store | min_index: new_min_index, max_index: new_max_index}
true ->
# To avoid shifting too often when nearing the capacity of the array
# we may grow it before we actually reach the capacity
new_length = get_new_length(new_min_index, new_max_index)
if new_length > :array.size(store.bins) do
store = %{store | bins: :array.resize(new_length, store.bins)}
adjust(store, new_min_index, new_max_index)
else
adjust(store, new_min_index, new_max_index)
end
end
end
@spec adjust(t(), integer(), integer()) :: t()
defp adjust(store, new_min_index, new_max_index) do
center_counts(store, new_min_index, new_max_index)
end
@spec center_counts(t(), integer(), integer()) :: t()
defp center_counts(store, new_min_index, new_max_index) do
mid_index = new_min_index + div(new_max_index - new_min_index + 1, 2)
store = shift_counts(store, store.offset + div(:array.size(store.bins), 2) - mid_index)
%{store | min_index: new_min_index, max_index: new_max_index}
end
@spec shift_counts(t(), integer()) :: t()
defp shift_counts(store, shift) do
new_array =
store.bins
|> :array.size()
|> :array.new([{:fixed, true}, {:default, 0}])
new_array =
store.bins
|> :array.sparse_to_orddict()
|> Enum.reduce(new_array, fn {k, v}, new_array ->
:array.set(k + shift, v, new_array)
end)
%{store | bins: new_array, offset: store.offset - shift}
end
@doc """
Checks if the store has any information in it.
## Examples
iex> store = Dense.new()
...> Dense.empty?(store)
true
iex> store = Dense.add(Dense.new(), 754)
...> Dense.empty?(store)
false
"""
@impl Datadog.Sketch.Store
@spec empty?(t()) :: bool()
def empty?(%{count: 0.0}), do: true
def empty?(_store), do: false
@doc """
Returns the total amount of counts stored.
## Examples
iex> store = Dense.new()
...> Dense.total_count(store)
0.0
iex> store = Dense.add(Dense.new(), 754)
...> Dense.total_count(store)
1.0
iex> store = Dense.add_with_count(Dense.new(), 754, 42.42)
...> Dense.total_count(store)
42.42
# Verified against golang implementation
iex> store = Dense.add_bins(Dense.new(), [
...> %{index: 4, count: 12.48},
...> %{index: 65, count: 12.48},
...> %{index: 37, count: 847.4}
...> ])
...> Dense.total_count(store)
872.36
"""
@impl Datadog.Sketch.Store
@spec total_count(t()) :: float()
def total_count(%{count: count}), do: count
@doc """
Returns the minimum index of the store.
## Examples
iex> store = Dense.new()
...> Dense.min_index(store)
0
# Verified against golang implementation
iex> store = Dense.add_bins(Dense.new(), [
...> %{index: 4, count: 12.48},
...> %{index: 65, count: 12.48},
...> %{index: 37, count: 847.4}
...> ])
...> Dense.min_index(store)
4
"""
@impl Datadog.Sketch.Store
@spec min_index(t()) :: integer()
def min_index(%{count: 0.0}), do: 0
def min_index(%{min_index: min_index}), do: min_index
@doc """
Returns the maximum index of the store.
## Examples
iex> store = Dense.new()
...> Dense.max_index(store)
0
iex> store = Dense.add(Dense.new(), 128)
...> Dense.max_index(store)
128
# Verified against golang implementation
iex> store = Dense.add_bins(Dense.new(), [
...> %{index: 4, count: 12.48},
...> %{index: 65, count: 12.48},
...> %{index: 37, count: 847.4}
...> ])
...> Dense.max_index(store)
65
"""
@impl Datadog.Sketch.Store
@spec max_index(t()) :: integer()
def max_index(%{count: 0.0}), do: 0
def max_index(%{max_index: max_index}), do: max_index
@doc """
Return the key for the value at rank.
## Examples
# Matches the golang implementation when no data is present.
iex> store = Dense.new()
...> Dense.key_at_rank(store, 0.0)
-134_217_729
# Verified matching to golang implementation
iex> store = Dense.add(Dense.new(), 128)
...> Dense.key_at_rank(store, 0.0)
128
# Verified matching to golang implementation
iex> store = Dense.add_bins(Dense.new(), [
...> %{index: 12, count: 423.43},
...> %{index: 244, count: 1238.123},
...> %{index: 124, count: 2184.124}
...> ])
...> Dense.key_at_rank(store, 64.0)
12
"""
@impl Datadog.Sketch.Store
@spec key_at_rank(t(), float()) :: integer()
def key_at_rank(store, rank) when rank < 0.0,
do: key_at_rank(store, 0.0)
def key_at_rank(store, rank) do
{step, result} =
store.bins
|> :array.sparse_to_orddict()
|> Enum.reduce_while({:not_end, 0.0}, fn {i, b}, {step, n} ->
n = n + b
if n > rank do
{:halt, {:end, i + store.offset}}
else
{:cont, {step, n}}
end
end)
case step do
:end -> result
:not_end -> store.max_index
end
end
@doc """
Returns a struct for Protobuf encoding. Used for sending data to
Datadog.
## Examples
# Verified matching to golang implementation
iex> store = Dense.add(Dense.new(), 4)
...> Dense.to_proto(store)
%Datadog.Sketch.Protobuf.Store{
binCounts: %{},
contiguousBinCounts: [1.0],
contiguousBinIndexOffset: 4
}
# Verified matching to golang implementation
iex> store = Dense.add_bins(Dense.new(), [
...> %{index: 4, count: 12.48},
...> %{index: 65, count: 12.48},
...> %{index: 37, count: 847.4}
...> ])
...> Dense.to_proto(store)
%Datadog.Sketch.Protobuf.Store{
binCounts: %{},
contiguousBinCounts: [12.48, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 847.4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 12.48],
contiguousBinIndexOffset: 4
}
"""
@impl Datadog.Sketch.Store
@spec to_proto(t()) :: Datadog.Sketch.Protobuf.Store.t()
def to_proto(%{count: 0.0}), do: %Datadog.Sketch.Protobuf.Store{contiguousBinCounts: nil}
def to_proto(store) do
new_length = store.max_index - store.min_index + 1
new_array = :array.new(new_length, [{:fixed, true}, {:default, 0}])
new_array =
store.bins
|> :array.sparse_to_orddict()
|> Enum.reduce(new_array, fn {k, v}, new_array ->
:array.set(k + store.offset - store.min_index, v, new_array)
end)
%Datadog.Sketch.Protobuf.Store{
contiguousBinCounts: :array.to_list(new_array),
contiguousBinIndexOffset: store.min_index
}
end
@doc """
Maps over all values and multiplies by the given weight.
## Examples
# Verified matching to golang implementation
iex> store = Dense.add_bins(Dense.new(), [
...> %{index: 4, count: 10.0},
...> %{index: 2, count: 20.0},
...> %{index: 6, count: 30.0}
...> ])
...> store = Dense.reweight(store, 2)
...> Dense.total_count(store)
120.0
"""
@impl Datadog.Sketch.Store
@spec reweight(t(), float()) :: t()
def reweight(store, weight) do
new_bins = :array.sparse_map(fn _i, v -> v * weight end, store.bins)
%{store | bins: new_bins, count: store.count * weight}
end
end
defimpl Enumerable, for: Datadog.Sketch.Store.Dense do
def count(store) do
length =
store.bins
|> :array.sparse_to_orddict()
|> length()
{:ok, length}
end
def member?(_store, _value), do: {:error, __MODULE__}
def slice(_store), do: {:error, __MODULE__}
def reduce(store, acc, fun) do
store.bins
|> :array.sparse_to_orddict()
|> Enum.map(fn {k, v} -> {k + store.offset, v} end)
|> Enumerable.List.reduce(acc, fun)
end
end
