[tarantool-patches] Re: [PATCH 2/3] Add surrogate ID for BINARY collation

[n.pettik]

I have occasionally sent mail from wrong address, so
you might miss it. My apologies, I resend it from right one.

> On 1 Nov 2018, at 19:31, Никита Петтик <kitnerh at gmail.com> wrote:
> 
>> On 1 Nov 2018, at 18:39, Konstantin Osipov <kostja at tarantool.org> wrote:
>> 
>> * n.pettik <korablev at tarantool.org> [18/11/01 16:11]:
>>>>> I guess, because
>>>>> 
>>>>> 1) It is not real collation and is not presented in
>>>>> _collation. So for a user it would be strange to see
>>>>> a gap between 2 and 4 in _collation, which can not be
>>>>> set.
>>>> 
>>>> Let's insert it there.
>>> 
>>> So, you insist on id == 3, right? Again, if user process select
>>> rom _collation space, one won’t see entry with id == 3.
>>> On the other hand, if user attempts at inserting id == 3,
>>> one will get an error.
>> 
>> No, I don't insist yet. Why not insert a special row in there?
> 
> Because insertion to _collation would result in creation
> of collation objects. Meanwhile, in fact we need only ID
> to distinguish BINARY and no-collation. The rest is the
> same for them. So, it makes sense to store only ID within
> space format. That is my point.
> 
>>>>> is consistent to has its ID near COLL_NONE, in a "special
>>>>> range" of collation identifiers.
>>>> 
>>>> Uhm, AFAIU we have two binary collations. One is "collation is not
>>>> set" and another is "collation binary". Which one did you mean
>>>> now?
>>> 
>>> FIrst one is not collation at all. It is rather “absence” of any collation.
>>> The second one is sort of “surrogate” and in terms of functionality
>>> means the same. However, its id will be stored in space format in
>>> order to indicate that BINARY collation should be forced during
>>> comparisons.
>> 
>> I think we could use internal ids to reference both cases. For
>> these both ids we could have surrogate rows in _coll system space,
>> they won't harm. This will make things easier in the future. 
> 
> Ok,  how do you suggest to call “absence” of collation? Like this:
> 
> box.space._collation:select()
> 
> ---
> - - [1, 'unicode', 1, 'ICU', '', {}]
>  - [2, 'unicode_ci', 1, 'ICU', '', {'strength': 'primary’}]
>  - [3, ‘none', 1, 'ICU', '', {}]
> ...
> 
> It is nonsense, IMHO. No collation is like “no collation at all” -
> nothing represents it, especially visible for user. With BINARY
> collation it would look even more suspicious:
> 
> - - [1, 'unicode', 1, 'ICU', '', {}]
>  - [2, 'unicode_ci', 1, 'ICU', '', {'strength': 'primary’}]
>  - [3, ‘none', 1, 'ICU', '', {}]
>  - [4, ‘binary', 1, 'ICU', '', {}]
> 
> It would confuse users who don’t use SQL: in Tarantool NoSQL
> there is no difference between “binary” and “no-collation”.
> Moreover, to keep things consistent, we would have to 	make
> default collation be ’none’ instead of absence of collation.
> It means that field def without explicitly set collation would
> have ’none’ collation in format. For instance:
> 
> *before*
> 
> - [{'affinity': 66, 'type': ’string', 'nullable_action': 'abort', 'name': 'ID', 'is_nullable': false}]
> 
> *after*
> 
> - [{'collation': 3, 'affinity': 66, 'type': 'string', 'nullable_action': 'abort',
>    'name': 'ID', 'is_nullable': false}]
> 
>> This is going to be the same mess as with NO ACTION and DEFAULT,
>> which are mostly the same, but not quite, so we'd better prepare.
> 
> It is considered to be mess due to SQLite legacy. On the other hand, all
> these manipulations with collations follow SQL ANSI.
> 
> All points considered, I would prefer to introduce only another one ID
> (alongside with COLL_NONE ID) and prohibit to create collations with
> these ids. OR, add surrogate “binary collation” to _collation with id == 3,
> but not both “binary” and “none”.

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