read0read.ic

来自「这是linux下运行的mysql软件包,可用于linux 下安装 php + m」· IC 代码 · 共 81 行

/******************************************************
Cursor read

(c) 1997 Innobase Oy

Created 2/16/1997 Heikki Tuuri
*******************************************************/

/*************************************************************************
Gets the nth trx id in a read view. */
UNIV_INLINE
dulint
read_view_get_nth_trx_id(
/*=====================*/
				/* out: trx id */
	read_view_t*	view,	/* in: read view */
	ulint		n)	/* in: position */
{
	ut_ad(n < view->n_trx_ids);

	return(*(view->trx_ids + n));
}

/*************************************************************************
Sets the nth trx id in a read view. */
UNIV_INLINE
void
read_view_set_nth_trx_id(
/*=====================*/
	read_view_t*	view,	/* in: read view */
	ulint		n,	/* in: position */
	dulint		trx_id)	/* in: trx id to set */
{
	ut_ad(n < view->n_trx_ids);

	*(view->trx_ids + n) = trx_id;
}

/*************************************************************************
Checks if a read view sees the specified transaction. */
UNIV_INLINE
ibool
read_view_sees_trx_id(
/*==================*/
				/* out: TRUE if sees */
	read_view_t*	view,	/* in: read view */
	dulint		trx_id)	/* in: trx id */
{
	ulint	n_ids;
	int	cmp;
	ulint	i;
	
	if (ut_dulint_cmp(trx_id, view->up_limit_id) < 0) {

		return(TRUE);
	}

	if (ut_dulint_cmp(trx_id, view->low_limit_id) >= 0) {

		return(FALSE);
	}

	/* We go through the trx ids in the array smallest first: this order
	may save CPU time, because if there was a very long running
	transaction in the trx id array, its trx id is looked at first, and
	the first two comparisons may well decide the visibility of trx_id. */

	n_ids = view->n_trx_ids;

	for (i = 0; i < n_ids; i++) {

		cmp = ut_dulint_cmp(trx_id,
				read_view_get_nth_trx_id(view, n_ids - i - 1));
		if (cmp <= 0) {
			return(cmp < 0);
		}
	}
	
	return(TRUE);
}