Optimize RowBinary map input encoding (#399)

* Optimize RowBinary map encoding

* Use direct map fold for RowBinary encoding

* Inline map fold callback

* simpler

* Test empty map iodata output

* Add RowBinary encode test helper

Author: ruslandoga

lib/ch/row_binary.ex

@@ -316,7 +316,13 @@ defmodule Ch.RowBinary do
     [encode(:varint, length(m)) | encode_many_kv(m, k, v)]
   end
 
-  def encode({:map, _k, _v} = t, m) when is_map(m), do: encode(t, Map.to_list(m))
+  def encode({:map, k, v}, m) when is_map(m) do
+    [
+      encode(:varint, map_size(m))
+      | :maps.fold(fn key, value, acc -> [encode(k, key), encode(v, value) | acc] end, [], m)
+    ]
+  end
+
   def encode({:map, _k, _v}, []), do: 0
   def encode({:map, _k, _v}, nil), do: 0
 

test/ch/row_binary_test.exs

@@ -4,6 +4,10 @@ defmodule Ch.RowBinaryTest do
   import Ch.RowBinary
   import Bitwise
 
+  defp encode_to_binary(type, value) do
+    type |> encode(value) |> IO.iodata_to_binary()
+  end
+
   test "encode -> decode" do
     spec = [
       {:string, ""},
@@ -167,7 +171,8 @@ defmodule Ch.RowBinaryTest do
 
     test "map" do
       assert encode({:map, :string, :string}, []) == 0
-      assert encode({:map, :string, :string}, %{}) == 0
+
+      assert encode_to_binary({:map, :string, :string}, %{}) == <<0>>
 
       assert encode({:map, :string, :string}, %{"hello" => "world"}) ==
                encode({:map, :string, :string}, [{"hello", "world"}])
@@ -237,7 +242,7 @@ defmodule Ch.RowBinaryTest do
 
   test "strings preserve raw bytes" do
     value = "\x61\xF0\x80\x80\x80b"
-    str = IO.iodata_to_binary(encode(:string, value))
+    str = encode_to_binary(:string, value)
 
     assert decode_rows(str, [:string]) == [[value]]