mvcc: insert-after-delete in single transaction may cause duplicates in secondary indexes

[Astronomax]

Bug description

Transaction with is_own_change = true may result in duplicate.

This check skips the second transaction, considering that it cannot lead to duplicates. But it's wrong.

tarantool/src/box/memtx_tx.c

Lines 2841 to 2843 in e6ec4aa

	if (test_stmt->is_own_change &&
	test_stmt->del_story == NULL)
	continue;

Steps to reproduce

Run the following reproducer.lua script:

fiber = require('fiber')

box.cfg{memtx_use_mvcc_engine=true}

box.schema.space.create("test")
box.space.test:format{{'a', type='unsigned'}, {'b', type='unsigned'}}
box.space.test:create_index("pk", {parts={{'a'}}})
box.space.test:create_index("sk", {parts={{'b'}}, unique=true})

box.space.test:truncate()

f1 = fiber.create(function()
	box.begin()
	box.space.test:replace{1, 3}
	fiber.sleep(1)
	box.commit()
end)
f1:set_joinable(true)

f2 = fiber.create(function()
	box.begin()
	box.space.test:replace{4, 4}
	box.space.test:delete{4}
	box.space.test:replace{4, 3}
	fiber.sleep(2)
	box.commit()
end)
f2:set_joinable(true)

local ok, err = f1:join()
print(ok, err)

ok, err = f2:join()
print(ok, err)

print(require('yaml').encode(box.space.test:select{}))

box.space.test:drop()
os.exit()

How to run:

$ tarantool -i reproducer.lua

Actual output:

---
- [1, 3]
- [4, 3]
...

Actual behavior

Duplicates appear in secondary index.

Expected behavior

No duplicates appear in secondary index (the second transaction must be rolled back).