Re: [PATCH v2 2/2] alter: zap space_vtab::commit_alter

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Fri, Apr 06, 2018 at 05:10:01PM +0300, Konstantin Osipov wrote:
> * Vladimir Davydov <vdavydov.dev@gmail.com> [18/04/06 16:20]:
> 
> > space_vtab::commit_alter is implemented only by memtx, which uses it
> > to set bsize for a new space. However, it isn't necessary to use
> > commit_alter for this - instead we can set bsize in prepare_alter and
> > reset it in drop_primary_key, along with memtx_space::replace. Let's
> > do it and zap space_vtab::commit_alter altogether, because the callback
> > is confusing: judging by its name it should be called after WAL write,
> > but it is called before.
> >  void
> >  DropIndex::alter(struct alter_space *alter)
> >  {
> > -	/*
> > -	 * If it's not the primary key, nothing to do --
> > -	 * the dropped index didn't exist in the new space
> > -	 * definition, so does not exist in the created space.
> > -	 */
> > -	if (space_index(alter->new_space, 0) != NULL)
> > -		return;
> > -	/*
> > -	 * OK to drop the primary key. Inform the engine about it,
> > -	 * since it may have to reset handler->replace function,
> > -	 * so that:
> > -	 * - DML returns proper errors rather than crashes the
> > -	 *   program
> > -	 * - when a new primary key is finally added, the space
> > -	 *   can be put back online properly.
> > -	 */
> > -	space_drop_primary_key(alter->new_space);
> > +	if (old_index_def->iid == 0)
> > +		space_drop_primary_key(alter->new_space);
> >  }
> 
> I keep wondering why you ditched a nice comment.
> If you think it was bad, please write a better one.

This comment is only pertinent to memtx so I just moved it to
memtx_space_drop_primary_key.

Regarding DropIndex::alter() - the code is pretty self-explaining there
(call drop_primary_key if the primary key is dropped) and doesn't need
any comments IMO.

> 
> The patch is OK to push after putting back the previous or adding
> a new good comment.