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 Tue, 16 Jun 2020 15:10:39 +0300 (MSK)
References: <50a25fbae907f1b0d5406fb2e78d40d3e42a8a8d.1591029888.git.korablev@tarantool.org>
From: Aleksandr Lyapunov <alyapunov@tarantool.org>
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Date: Tue, 16 Jun 2020 15:10:38 +0300
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Subject: Re: [Tarantool-patches] [PATCH v2] vinyl: restart read iterator in
 case of rolled back WAL
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To: Nikita Pettik <korablev@tarantool.org>, tarantool-patches@dev.tarantool.org
Cc: v.shpilevoy@tarantool.org

Thanks for the patch! See my 2 comments below:

On 6/1/20 7:46 PM, Nikita Pettik wrote:
>   
> +	if (vy_mem_tree_iterator_is_invalid(&src->mem_iterator.curr_pos)) {
> +		assert(src->mem_iterator.curr.stmt == NULL);
> +		return 1;
> +	}
I'm afraid that the iterator will not always be invalid in the given case.
As I see, if a mem holds any older tuple with the same key (e.g. older
version of that tuple), the restoration routine will find the older tuple
with the non-invalid iterator.
I also think that mem_restore must handle all the possible data
changes by itself without concern of read_iterator.
> -	if (vy_read_iterator_restore_mem(itr, &next) != 0)
> +	int rc = vy_read_iterator_restore_mem(itr, &next);
> +	if (rc < 0)
>   		return -1;
> +	if (rc > 0) {
> +		vy_read_iterator_restore(itr);
> +		goto restart;
> +	}
The read iterator was rewritten several times and still have at least
several bugs. I think we should admit that we cannot support such a
complicated solution. How about some stupid solution: if ANY change
has been happened during yield - restart advancing?