[tarantool-patches] box: disable sparse optimization in box.tuple.new()

[Kirill Shcherbatov <kshcherbatov@tarantool.org>]

The box.tuple.new() used to call luamp_encode_tuple with
default LUA serializer config 'luaL_msgpack_default'. This
routine may consider an array to be excessively sparse when
  + encode_sparse_ratio > 0
  + max(table) > encode_sparse_safe
  + max(table) > count(table) * encode_sparse_ratio.
Sparse optimization save memory via representing excessively
sparse tuple as MP_MAP. But Tarantool tuple always must be
MP_ARRAY so it is not relevant for box.tuple.new semantics.
So it is disabled with encode_sparse_ratio = 0 in a new local
serializer config.

Closes #3882
---
 src/box/lua/tuple.c     |  9 ++++++++
 test/box/tuple.result   | 50 +++++++++++++++++++++++++++++++++++++++++
 test/box/tuple.test.lua | 26 +++++++++++++++++++++
 3 files changed, 85 insertions(+)

diff --git a/src/box/lua/tuple.c b/src/box/lua/tuple.c
index 756856f4e..52fb79d5b 100644
--- a/src/box/lua/tuple.c
+++ b/src/box/lua/tuple.c
@@ -108,8 +108,17 @@ lbox_tuple_new(lua_State *L)
 		      luamp_error, L);
 
 	if (argc == 1 && (lua_istable(L, 1) || luaT_istuple(L, 1))) {
+		/**
+		 * Disable storage optimization for excessively
+		 * sparse arrays as a tuple always must be regular
+		 * MP_ARRAY.
+		 */
+		int encode_sparse_ratio =
+			luaL_msgpack_default->encode_sparse_ratio;
+		luaL_msgpack_default->encode_sparse_ratio = 0;
 		/* New format: box.tuple.new({1, 2, 3}) */
 		luamp_encode_tuple(L, luaL_msgpack_default, &stream, 1);
+		luaL_msgpack_default->encode_sparse_ratio = encode_sparse_ratio;
 	} else {
 		/* Backward-compatible format: box.tuple.new(1, 2, 3). */
 		mpstream_encode_array(&stream, argc);
diff --git a/test/box/tuple.result b/test/box/tuple.result
index b42012485..16aa66b1a 100644
--- a/test/box/tuple.result
+++ b/test/box/tuple.result
@@ -1164,3 +1164,53 @@ test_run:cmd("clear filter")
 ---
 - true
 ...
+--
+-- gh-3882: Inappropriate storage optimization for sparse arrays
+--          in box.tuple.new.
+--
+t = {}
+---
+...
+t[1] = 1
+---
+...
+t[2] = 2
+---
+...
+t[11] = 11
+---
+...
+box.tuple.new(t)
+---
+- [1, 2, null, null, null, null, null, null, null, null, 11]
+...
+s2 = box.schema.space.create('test')
+---
+...
+test_run:cmd("setopt delimiter ';'")
+---
+- true
+...
+s2:format({{name="a", type="str"}, {name="b", type="str", is_nullable=true},
+           {name="c", type="str", is_nullable=true},
+           {name="d", type="str", is_nullable=true},
+           {name="e", type="str", is_nullable=true},
+           {name="f", type="str", is_nullable=true},
+           {name="g", type="str", is_nullable=true},
+           {name="h", type="str", is_nullable=true},
+           {name="i", type="str", is_nullable=true},
+           {name="j", type="str", is_nullable=true},
+           {name="k", type="str", is_nullable=true}});
+---
+...
+test_run:cmd("setopt delimiter ''");
+---
+- true
+...
+s2:frommap({a="1", k="11"})
+---
+- ['1', null, null, null, null, null, null, null, null, null, '11']
+...
+s2:drop()
+---
+...
diff --git a/test/box/tuple.test.lua b/test/box/tuple.test.lua
index 276bb0f67..0c89feace 100644
--- a/test/box/tuple.test.lua
+++ b/test/box/tuple.test.lua
@@ -384,3 +384,29 @@ t2 = box.tuple.new(2)
 t1 = t1:update{{'+', 1, 1}}
 
 test_run:cmd("clear filter")
+
+--
+-- gh-3882: Inappropriate storage optimization for sparse arrays
+--          in box.tuple.new.
+--
+t = {}
+t[1] = 1
+t[2] = 2
+t[11] = 11
+box.tuple.new(t)
+
+s2 = box.schema.space.create('test')
+test_run:cmd("setopt delimiter ';'")
+s2:format({{name="a", type="str"}, {name="b", type="str", is_nullable=true},
+           {name="c", type="str", is_nullable=true},
+           {name="d", type="str", is_nullable=true},
+           {name="e", type="str", is_nullable=true},
+           {name="f", type="str", is_nullable=true},
+           {name="g", type="str", is_nullable=true},
+           {name="h", type="str", is_nullable=true},
+           {name="i", type="str", is_nullable=true},
+           {name="j", type="str", is_nullable=true},
+           {name="k", type="str", is_nullable=true}});
+test_run:cmd("setopt delimiter ''");
+s2:frommap({a="1", k="11"})
+s2:drop()
-- 
2.20.1