Re: [Tarantool-patches] [PATCH 1/2] tuple: fix multikey field JSON access crash

[Oleg Babin <olegrok@tarantool.org>]

Hi! Thanks for your patch. It's not a review but I have a question.

On 05/08/2020 02:45, Vladislav Shpilevoy wrote:
> When a tuple had format with multikey indexes in it, any attempt
> to get a multikey indexed field by a JSON path from Lua led to a
> crash.
>
> That was because of incorrect interpretation of offset slot value
> in tuple's field map.
>
> Tuple field map is an array stored before the tuple's MessagePack
> data. Each element is a 4 byte offset to an indexed value to be
> able to get it for O(1) time without MessagePack decoding of all
> the previous fields.
>
> At least it was so before multikeys. Now tuple field map is not
> just an array. It is rather a 2-level array, somehow similar to
> ext4 FS. Some elements of the root array are positive numbers
> pointing at data. Some elements point at a second 'indirect'
> array, so called 'extra', size of which is individual for each
> tuple. These second arrays are used by multikey indexes to store
> offsets to each multikey indexed value in a tuple.


Do json path updates use offsets? Is such issue relevant for them?

I tried to update poisoned tuple but seems it works fine. But maybe I've 
missed something.