Re: [Tarantool-patches] [PATCH 1/6] sql: refactor resulting set metadata

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

Hi! Thanks for the patch!

How is your life, kids, wife, job? I hope everything
is good! Lets consider what can we do better here.
Below is just my own opinion and some of advice, nothing
obligatory or toxic!

See 6 tiny friendly comments below :) (no dot in the end = no toxic)

On 27/11/2019 13:15, Nikita Pettik wrote:
> Move names and types of resulting set to a separate structure. Simplify
> their storage by introducing separate members for name and type
> (previously names and types were stored in one char * array). It will
> allow us to add new metadata properties with ease.
> 
> Needed for #4407
> ---
>  src/box/sql/delete.c  |  6 ++--
>  src/box/sql/insert.c  |  5 ++--
>  src/box/sql/legacy.c  |  2 +-
>  src/box/sql/pragma.c  | 14 ++++-----
>  src/box/sql/prepare.c |  9 +++---
>  src/box/sql/select.c  | 60 ++++++++++++++++++--------------------
>  src/box/sql/update.c  |  6 ++--
>  src/box/sql/vdbe.h    | 28 ++++++++++--------
>  src/box/sql/vdbeInt.h |  8 ++++-
>  src/box/sql/vdbeapi.c | 81 +++++++++------------------------------------------
>  src/box/sql/vdbeaux.c | 81 +++++++++++++++++++++++++++------------------------
>  11 files changed, 124 insertions(+), 176 deletions(-)
> 
> diff --git a/src/box/sql/prepare.c b/src/box/sql/prepare.c
> index 0ecc676e2..2d3466cc7 100644
> --- a/src/box/sql/prepare.c
> +++ b/src/box/sql/prepare.c
> @@ -146,11 +146,10 @@ sqlPrepare(sql * db,	/* Database handle. */
>  		sqlVdbeSetNumCols(sParse.pVdbe, name_count);
>  		for (int i = 0; i < name_count; i++) {
>  			int name_index = 2 * i + name_first;
> -			sqlVdbeSetColName(sParse.pVdbe, i, COLNAME_NAME,
> -					  azColName[name_index], SQL_STATIC);
> -			sqlVdbeSetColName(sParse.pVdbe, i, COLNAME_DECLTYPE,
> -					  azColName[name_index + 1],
> -					  SQL_STATIC);
> +			vdbe_set_metadata_col_name(sParse.pVdbe, i,
> +					  azColName[name_index]);
> +			vdbe_set_metadata_col_type(sParse.pVdbe, i,
> +					  azColName[name_index + 1]);

1. Lets fix this indentation.

>  		}
>  	}
>  
> diff --git a/src/box/sql/select.c b/src/box/sql/select.c
> index 8f93edd16..d6b8a158f 100644
> --- a/src/box/sql/select.c
> +++ b/src/box/sql/select.c
> @@ -2828,7 +2824,7 @@ multiSelect(Parse * pParse,	/* Parsing context */
>  						Select *pFirst = p;
>  						while (pFirst->pPrior)
>  							pFirst = pFirst->pPrior;
> -						generateColumnNames(pParse,
> +						generate_column_metadata(pParse,
>  								    pFirst->pSrc,
>  								    pFirst->pEList);

2. And this too.

>  					}
> diff --git a/src/box/sql/vdbe.h b/src/box/sql/vdbe.h
> index 582d48a1f..4142fb6ba 100644
> --- a/src/box/sql/vdbe.h
> +++ b/src/box/sql/vdbe.h
> @@ -248,7 +241,18 @@ void sqlVdbeResetStepResult(Vdbe *);
>  void sqlVdbeRewind(Vdbe *);
>  int sqlVdbeReset(Vdbe *);
>  void sqlVdbeSetNumCols(Vdbe *, int);
> -int sqlVdbeSetColName(Vdbe *, int, int, const char *, void (*)(void *));
> +
> +/**
> + * Set the name of the idx'th column to be returned by the SQL
> + * statement. @name must be a pointer to a nul terminated string.
> + * This call must be made after a call to sqlVdbeSetNumCols().
> + */
> +int
> +vdbe_set_metadata_col_name(struct Vdbe *v, int col_idx, const char *name);
> +
> +int
> +vdbe_set_metadata_col_type(struct Vdbe *v, int col_idx, const char *type);

3. I think, that we should use one prefix for metadata
methods. You used 'vdbe_metadata_delete()' above, so lets
make it 'vdbe_metadata_*' everywhere. And these functions
will be

    vdbe_metadata_set_col_name/type...

> diff --git a/src/box/sql/vdbeInt.h b/src/box/sql/vdbeInt.h
> index 0f32b4cd6..9ab3753cb 100644
> --- a/src/box/sql/vdbeInt.h
> +++ b/src/box/sql/vdbeInt.h
> @@ -394,7 +399,8 @@ struct Vdbe {
>  	Op *aOp;		/* Space to hold the virtual machine's program */
>  	Mem *aMem;		/* The memory locations */
>  	Mem **apArg;		/* Arguments to currently executing user function */
> -	Mem *aColName;		/* Column names to return */
> +	/** SQL metadata for SELECT queries. */

4. Looks like it can be emitted on DML too. I see
vdbe_set_metadata_col_name(v, 0, "rows updated") in
sqlUpdate(), and vdbe_set_metadata_col_name(v, 0, "rows deleted")
in sql_table_delete_from().

> +	struct sql_column_metadata *metadata;
>  	Mem *pResultSet;	/* Pointer to an array of results */
>  	VdbeCursor **apCsr;	/* One element of this array for each open cursor */
>  	Mem *aVar;		/* Values for the OP_Variable opcode. */
> diff --git a/src/box/sql/vdbeaux.c b/src/box/sql/vdbeaux.c
> index a1d658648..db11fbf33 100644
> --- a/src/box/sql/vdbeaux.c
> +++ b/src/box/sql/vdbeaux.c
> @@ -1827,6 +1827,18 @@ Cleanup(Vdbe * p)
>  	p->pResultSet = 0;
>  }
>  
> +void
> +vdbe_metadata_delete(struct Vdbe *v)
> +{
> +	if (v->metadata != NULL) {
> +		for (int i = 0; i < v->nResColumn; ++i) {
> +			free((void *)v->metadata[i].name);
> +			free((void *)v->metadata[i].type);

5. The necessity to do that cast basically makes 'const'
in the struct useless. Could you please make them just
char *, not const char *?

> +		}
> +		free(v->metadata);
> +	}
> +}
> +
>  /*
>   * Set the number of result columns that will be returned by this SQL
>   * statement. This is now set at compile time, rather than during
> @@ -1836,50 +1848,44 @@ Cleanup(Vdbe * p)
> +vdbe_set_metadata_col_name(struct Vdbe *p, int idx, const char *name)
> +{
>  	assert(idx < p->nResColumn);
> -	assert(var < COLNAME_N);
> -	if (p->db->mallocFailed) {
> -		assert(!zName || xDel != SQL_DYNAMIC);
> +	if (p->metadata[idx].name != NULL)
> +		free((void *)p->metadata[idx].name);
> +	p->metadata[idx].name = strdup(name);
> +	if (p->metadata[idx].name == NULL) {
> +		diag_set(OutOfMemory, strlen(name), "strdup", "name");

6. Len + 1. Dup allocates terminating zero too. In the next patches
too.

>  		return -1;
>  	}
> -	assert(p->aColName != 0);
> -	assert(var == COLNAME_NAME || var == COLNAME_DECLTYPE);
> -	pColName = &(p->aColName[idx + var * p->nResColumn]);
> -	rc = sqlVdbeMemSetStr(pColName, zName, -1, 1, xDel);
> -	assert(rc != 0 || !zName || (pColName->flags & MEM_Term) != 0);
> -	return rc;
> +	return 0;
> +}
> +