[tarantool-patches] Re: [PATCH 1/4] sql: remove OP_AutoCommit opcode

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

Hello. Thanks for contributing! See 6 comments below.

1. OP_AutoCommit still exists in mkopcodeh.sh.

On 03/05/2018 21:49, Nikita Pettik wrote:
> In SQLite OP_AutoCommit opcode used to set transaction operation:
> BEGIN, ROLLBACK and COMMIT, switching auto-commit flag in VDBE.
> As for Tarantool, it is confusing, since there are some differences
> between auto-commit modes: 'INSERT ...  VALUES (1), (2), (3)' is one
> indivisible operation for SQLite, and three operations in real
> auto-commit mode for Tarantool. To simulate SQLite auto-commit mode,
> these three insertions are wrapped into one SEPARATE transaction,
> which is, in fact, not real autocommit mode.
> So, lets add separate explicit opcodes to BEGIN, ROLLBACK and COMMIT
> transactions as user's operations. Auto-commit mode is set once at VDBE
> creation and can be changed only by implicit opcode OP_TTransaction,
> which is added to each DML statement, or by 'BEGIN' SQL statement.
> ---
>   src/box/sql/build.c     |  51 +++++-------------
>   src/box/sql/main.c      |   3 +-
>   src/box/sql/parse.y     |  11 ++--
>   src/box/sql/sqliteInt.h |  31 +++++++++--
>   src/box/sql/vdbe.c      | 136 +++++++++++++++++++++++++-----------------------
>   src/box/sql/vdbeInt.h   |   3 +-
>   src/box/sql/vdbeapi.c   |   5 +-
>   src/box/sql/vdbeaux.c   |  34 ++++++------
>   8 files changed, 138 insertions(+), 136 deletions(-)
> 
> diff --git a/src/box/sql/vdbe.c b/src/box/sql/vdbe.c
> index 013460f79..cf2b769c7 100644
> --- a/src/box/sql/vdbe.c
> +++ b/src/box/sql/vdbe.c
> @@ -2875,7 +2875,7 @@ case OP_Savepoint: {
>   	/* Assert that the p1 parameter is valid. Also that if there is no open
>   	 * transaction, then there cannot be any savepoints.
>   	 */
> -	assert(psql_txn->pSavepoint == 0 || p->autoCommit == 0);
> +	assert(psql_txn->pSavepoint == 0 || box_txn());

2. Please, use explicit ==/!= NULL (pSavepoint is pointer).
> +/* Opcode: TransactionBegin * * * * *
> + *
> + * Start Tarantool's transaction.
> + * Only do that if there is no other active transactions.
> + * Otherwise, raise an error with appropriate error message.
> + */
> +case OP_TransactionBegin: {
> +	if (!box_txn()) {

3. sql_txn_begin() does this check for you. Here you can always call sql_txn_begin() and
check result code. After this you can remove manual error message creating, and just goto
abort_due_to_error. Error code is always SQL_TARANTOOL_ERROR.
> +
> +/* Opcode: TransactionCommit * * * * *
> + *
> + * Commit Tarantool's transaction.
> + * If there is no active transaction, raise an error.
> + */
> +case OP_TransactionCommit: {
> +	if (box_txn()) {
> +		if (box_txn_commit() != 0) {
> +			rc = SQL_TARANTOOL_ERROR;
> +			goto abort_due_to_error;
>   		}
> -		rc = SQLITE_DONE;
> -		goto vdbe_return;
>   	} else {
> -		sqlite3VdbeError(p,
> -				 (!desiredAutoCommit)?"cannot start a transaction within a transaction":(
> -					 (iRollback)?"cannot rollback - no transaction is active":
> -					 "cannot commit - no transaction is active"));
> +		sqlite3VdbeError(p, "cannot commit - no transaction is active");
> +		rc = SQLITE_ERROR;
> +		goto abort_due_to_error;

4. I am not sure, that we must throw on commit/rollback with no
transaction. In Lua it is ok. Possibly you should ask in the server team chat.
> @@ -3052,18 +3052,26 @@ case OP_AutoCommit: {
>   
>   /* Opcode: TTransaction * * * * *
>    *
> - * Start Tarantool's transaction.
> - * Only do that if auto commit mode is on. This should be no-op
> - * if this opcode was emitted inside a transaction.
> + * Start Tarantool's transaction, if there is no active
> + * transactions. Otherwise, create anonymous savepoint,
> + * which is used to correctly process ABORT statement inside
> + * outer transaction.
> + *
> + * In contrast to OP_TransactionBegin, this is service opcode,
> + * generated automatically alongside with DML routine.
>    */
>   case OP_TTransaction: {
> -	if (p->autoCommit) {
> -		rc = box_txn_begin() == 0 ? SQLITE_OK : SQL_TARANTOOL_ERROR;
> -	}
> -	if (box_txn()
> -	    && p->autoCommit == 0){
> +	if (!box_txn()) {
> +		if (box_txn_begin() != 0) {

5. Same as 3. If you need error code, then use box_error_code() when begin() fails.

> diff --git a/src/box/sql/vdbeaux.c b/src/box/sql/vdbeaux.c
> index b3998ea27..0bd0d455b 100644
> --- a/src/box/sql/vdbeaux.c
> +++ b/src/box/sql/vdbeaux.c
> @@ -2477,31 +2477,27 @@ sqlite3VdbeCheckFk(Vdbe * p, int deferred)
>   int
>   sql_txn_begin(Vdbe *p)
>   {
> -	struct txn *ptxn;
> -
>   	if (in_txn()) {
>   		diag_set(ClientError, ER_ACTIVE_TRANSACTION);
> -		return -1;
> +		return SQL_TARANTOOL_ERROR;

6. It is step backwards to sqlite result codes style. Lets return 0/-1,
and set errors via diag_set. If sql_txn_begin() returns -1, it is always
SQL_TARANTOOL_ERROR.