Re: [tarantool-patches] Re: [PATCH v5 11/12] box: introduce offset slot cache in key_part

[Kirill Shcherbatov <kshcherbatov@tarantool.org>]

> I don't understand this comment. Could you please rephrase?
> I don't understand this statement either. Could you give an
> example?
> Did you consider storing it elsewhere, e.g. in some kind of 
> index search context?
Tuned tuple_field_by_part_raw routine with key_part's                        
offset_slot_cache. Introduced tuple_format epoch to test validity               
of this cache. The key_part caches last offset_slot source                      
format to make epoch comparison because same space may have                     
multiple format of same epoch that have different key_parts and                 
related offset_slots distribution.                                              
                                  
>> -	alter->new_space = space_new_xc(alter->space_def, &alter->key_list);
>> +	alter->new_space =
>> +		space_new_xc(alter->space_def, &alter->key_list,
>> +			     alter->old_space->format != NULL ?
>> +			     alter->old_space->format->epoch + 1 : 1);
> 
> Can't we make it simpler and simply increase epoch id every
> time we create a new space? This is only an optimization, 
> by leaking it into alter.cc you are making alter worry about
> stuff which should not be its concern.> Passing epoch id around explicitly is ugly.
The main problem we faced is that there are two formats in vinyl - regular
and disk format. Alter.cc does not know anything about the internal structure of
the vinyl space object, so he cannot update the disk epoch on his own.

> Why can't you do it in key_def_set_part?
> Lack of code reuse, abstraction leak.
Like this for now:
key_def_set_part(new_def, pos++, part->fieldno, part->type,
			   part->nullable_action, part->coll,
			   part->coll_id, part->sort_order, part->path,
			   part->path_len, part->offset_slot_cache,
			   part->format_cache);

> The source format to check that offset_slot_epoch is not stale.
> 
> Please avoid using the word "actuality".
"hit"