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 Tue,  7 Apr 2020 00:42:41 +0300 (MSK)
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From: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
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Date: Mon, 6 Apr 2020 23:42:39 +0200
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Subject: Re: [Tarantool-patches] [PATCH v2 1/1] sql: do not change order of
	inserted values
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To: imeevma@tarantool.org, tsafin@tarantool.org, tarantool-patches@dev.tarantool.org

Hi! Thanks for the patch!

See 2 questions below.

> diff --git a/src/box/sql.c b/src/box/sql.c
> index 27089bd..7c1eba2 100644
> --- a/src/box/sql.c
> +++ b/src/box/sql.c
> @@ -324,10 +324,17 @@ struct space *
>  sql_ephemeral_space_create(uint32_t field_count, struct sql_key_info *key_info)
>  {
>  	struct key_def *def = NULL;
> +	uint32_t part_count = field_count;
>  	if (key_info != NULL) {
>  		def = sql_key_info_to_key_def(key_info);
>  		if (def == NULL)
>  			return NULL;
> +		/*
> +		 * In case is_pk_rowid is true we can use rowid
> +		 * as the only part of the key.
> +		 */
> +		if (key_info->is_pk_rowid)
> +			part_count = 1;

1. On one hand this can really speed up ephemeral space comparators,
because we have special templates for single indexed unsigned field
if it is in 1, 2, or 3 column.

On the other hand this won't help, because rowid is the last column
somewhy. And these fast comparators won't help.

Can we make rowid first column?

>  	}
>  
>  	struct region *region = &fiber()->gc;
> @@ -364,17 +371,20 @@ sql_ephemeral_space_create(uint32_t field_count, struct sql_key_info *key_info)
>  		}
>  	}
>  
> -	for (uint32_t i = 0; i < field_count; ++i) {
> +	for (uint32_t i = 0; i < part_count; ++i) {
>  		struct key_part_def *part = &parts[i];
> -		part->fieldno = i;
> +		uint32_t j = i;
> +		if (key_info != NULL && key_info->is_pk_rowid)
> +			j = field_count - 1;

2. Does it make sense to use part count > 1, if we have rowid?
It is unique anyway.