Hi Sergei,


On 01/07/2016 08:53 PM, Sergei Golubchik wrote:
> Hi, Alexander!
>
> On Nov 27, Alexander Barkov wrote:
>>     Hi Serg,
>>
>> Please review a patch for MDEV-8092.
>
> I didn't review a lot of it, sorry. Because my first two comments - if
> we agree on them - might cause quite a few changes (search/replace kind
> of changes, but still). So I'd better look at the whole patch after
> that.

Sure. Thanks.

Please see below.

>
>> diff --git a/sql/field.h b/sql/field.h
>> index 0591914..a40e307 100644
>> --- a/sql/field.h
>> +++ b/sql/field.h
>> @@ -537,6 +537,115 @@ inline bool is_temporal_type_with_time(enum_field_types type)
>>   }
>>
>>
>> +/**
>> +  @class Name
>> +  An arbitrary SQL name, consisting of a NULL-terminated string
>> +  and its length.
>> +  Later it can be reused for table and schema names.
>> +*/
>> +class Name
>> +{
>> +  const char *m_str;
>> +  uint m_length;
>
> Sorry, we have too many "string" classes already.
> Either use LEX_STRING or create a Lex_string
> which is inherited from LEX_STRING, binary compatible with it
> and only adds C++ methods (and can be casted back and forth automatically).
> So that one could use Lex_string where a LEX_STRING is expected and vice
> versa

Sorry for a long reply.

This is a very convenient moment of time when
we can improve a few things. I disagree to go the easier way
with LEX_STRING.


LEX_STRING is a very unfortunately designed thing for the server side code.

It was a kind of Ok on 32 bit platforms.
But now on 64bit platforms it's just a waste of memory.
Length can never be large enough to use the entire "size_t".

Btw, it can even never be long enough to use "uint". It should be enough
to use uint16 for length and use the available remainder (6 bytes) to
store extra useful things, like string metadata.
It will help to avoid some operations, like character set conversion
in the client-server protocol, and I planned to add some optimization
in the future.


I propose to do the other way around:
- gradually get rid of using LEX_STRING and LEX_CSTRING for names
in the server side and use more suitable Name-alike classes instead.
- keep LEX_XXX only for compatibility with the existing pure C API,
   where it already presents now.


Please note, in the current patch version the Name class has
constructors that can accept LEX_STRING and LEX_CSTRING.
This means that you can pass LEX_STRING and LEX_CSTRING to any
function or method that is designed to accept Name,
and the patch already uses this. So this switch will go very smoothly.


As for "too many string classes", I have heard this a few times already,
both in MariaDB and earlier in Oracle :)
I don't agree with this statement.