Re: [PATCH 03/12] alter: move dictionary update from ModifySpace::alter_def to alter

[Konstantin Osipov <kostja@tarantool.org>]

* Vladimir Davydov <vdavydov.dev@gmail.com> [18/04/09 10:33]:
> -	struct tuple_dictionary *new_dict;
> -	/**
> -	 * Old tuple dictionary stored to rollback in destructor,
> -	 * if an exception had been raised after alter_def(), but
> -	 * before alter().
> -	 */
> -	struct tuple_dictionary *old_dict;
> +	struct tuple_dictionary *dict;

Please provide a comment. 

>  	/*
> -	 * Move new names into an old dictionary, which already is
> -	 * referenced by existing tuple formats. New dictionary
> -	 * object is deleted later, in destructor.
> +	 * Use the old dictionary for the new space, because
> +	 * it is already referenced by existing tuple formats.
> +	 * We will update it in place in ModifySpace::alter.
>  	 */

I don't understand this comment. Naming the variable "dict" didn't
help. Not having a comment for the variable where it was declared
didn't help :(

I do understand that your strategy is to swap the new space' dict
with the old space dict and hold the new space dict in a temp
variable until possible rollback. But I don't understand why you
had to change it. The changeset comment says nothing about
changing the way you modify the format, it only mentions changes
in the timing.

> -	new_dict = def->dict;
> -	old_dict = alter->old_space->def->dict;
> -	tuple_dictionary_swap(new_dict, old_dict);
> -	def->dict = old_dict;
> -	tuple_dictionary_ref(old_dict);
> +	dict = def->dict;
> +	def->dict = alter->old_space->def->dict;
> +	tuple_dictionary_ref(def->dict);
>  
>  	space_def_delete(alter->space_def);
>  	alter->space_def = def;
> @@ -959,21 +952,21 @@ ModifySpace::alter_def(struct alter_space *alter)
>  }
>  
>  void
> -ModifySpace::commit(struct alter_space *alter, int64_t signature)
> +ModifySpace::alter(struct alter_space *alter)
>  {
> -	(void) alter;
> -	(void) signature;
> -	old_dict = NULL;
> +	tuple_dictionary_swap(alter->new_space->def->dict, dict);
> +}
> +
> +void
> +ModifySpace::rollback(struct alter_space *alter)
> +{
> +	tuple_dictionary_swap(alter->new_space->def->dict, dict);
>  }
>  
>  ModifySpace::~ModifySpace()
>  {
> -	if (new_dict != NULL) {
> -		/* Return old names into the old dict. */
> -		if (old_dict != NULL)
> -			tuple_dictionary_swap(new_dict, old_dict);
> -		tuple_dictionary_unref(new_dict);
> -	}
> +	if (dict != NULL)
> +		tuple_dictionary_unref(dict);
>  	if (def != NULL)
>  		space_def_delete(def);
>  }
> diff --git a/src/box/tuple_format.c b/src/box/tuple_format.c
> index d3a7702d..11481473 100644
> --- a/src/box/tuple_format.c
> +++ b/src/box/tuple_format.c
> @@ -262,8 +262,6 @@ tuple_format_new(struct tuple_format_vtab *vtab, struct key_def * const *keys,
>  		 const struct field_def *space_fields,
>  		 uint32_t space_field_count, struct tuple_dictionary *dict)
>  {
> -	assert((dict == NULL && space_field_count == 0) ||
> -	       (dict != NULL && space_field_count == dict->name_count));
>  	struct tuple_format *format =
>  		tuple_format_alloc(keys, key_count, space_field_count, dict);
>  	if (format == NULL)
> -- 
> 2.11.0
> 

-- 
Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov