[Tarantool-patches] [PATCH] vinyl: add NULL check of xrow_upsert_execute() retval

[Vladislav Shpilevoy]

Note, I didn't see an error message in the log in the test below,
when it skipped the upsert.

> Here is a test. Create a tuple, and dump it on disk so as it would
> disappear from the memory level and from the cache:
> 
> 	box.cfg{}
> 	s = box.schema.create_space('test', {engine = 'vinyl'})
> 	pk = s:create_index('pk')
> 	s:insert({1, 1})
> 	box.snapshot()
> 
> Then restart (to ensure the cache is clear), and create 2 upserts:
> 
> 	box.cfg{}
> 	s = box.space.test
> 	ops = {}
> 	op = {'=', 2, 100}
> 	for i = 1, 2500 do table.insert(ops, op) end
> 	s:upsert({1}, ops)
> 	op = {'=', -1, 200}
> 	ops = {}
> 	for i = 1, 2500 do table.insert(ops, op) end
> 	s:upsert({1}, ops)
> 
> Now if I do select, I get
> 
> 	tarantool> s:select{}
> 	---
> 	- - [1, 200]
> 	...
> 
> But if I do dump + select, I get:
> 
> 	tarantool> box.snapshot()
> 	---
> 	- ok
> 	...
> 
> 	tarantool> s:select{}
> 	---
> 	- - [1, 100]
> 	...
> 
> During dump the second upsert was skipped even though it was valid.
>