Re: [Tarantool-patches] [PATCH v2 06/10] box: introduce stacked diagnostic area

[Nikita Pettik <korablev@tarantool.org>]

On 26 Mar 19:54, Konstantin Osipov wrote:
> * Nikita Pettik <korablev@tarantool.org> [20/03/25 09:32]:
> > +	/*
> > +	 * Make sure that adding error won't result in cycles.
> > +	 * Don't bother with sophisticated cycle-detection
> > +	 * algorithms, simple iteration is OK since as a rule
> > +	 * list contains a dozen errors at maximum.
> > +	 */
> > +	struct error *tmp = prev;
> > +	while (tmp != NULL) {
> > +		if (tmp == e)
> > +			return -1;
> > +		tmp = tmp->cause;
> > +	}
> 
> If you have to do it, better use rlist, rlist_del(e) rlist_add(e),
> this will make sure there are no cycles and the cost is constant.

rlist implementation is not really suitable for organizing errors
into list. See comment in the code:

	 * RLIST implementation is not really suitable here
	 * since it is organized as circular list. In such
	 * a case it is impossible to start an iteration
	 * from any node and finish at the logical end of the
	 * list.
 
> > +	if (prev != NULL) {
> > +		error_unlink_effect(prev);
> > +		prev->effect = e;
> > +		error_ref(prev);
> > +	}
> 
> cause and effect can be just wrappers around rlist_prev/next, if
> you have to. But error stack is not always cause and effect:
> imagine an SQL update which runs a bunch of triggers which all set
> add some errors to the diag, which one of these triggers errors is
> the cause of update error?.

I guess it is ok to stop execution after first trigger sets an error..?
They are fired one by one, not all at once.

> 
> -- 
> Konstantin Osipov, Moscow, Russia