> On 14 May 2019, at 21:41, Konstantin Osipov <kostja@tarantool.org> wrote:
> 
> * n.pettik <korablev@tarantool.org <mailto:korablev@tarantool.org>> [19/05/14 21:26]:
>>>> On 14 May 2019, at 20:00, Konstantin Osipov <kostja@tarantool.org> wrote:
>>>> 
>>>> * Kirill Shcherbatov <kshcherbatov@tarantool.org> [19/05/14 18:04]:
>>>>> @v.shpilevoy
>>>>>> Yes, I will. Kirill, please, send it again in a new thread. You can keep
>>>>>> version 3 and omit change list.
>>>>> 
>>>>> @kostya
>>>>>> It's better to fetch the bound field upon first access.
>>>>>> Most paths of the CHECK constraint may not touch most of the
>>>>>> fields.
>>>>> I have no idea, how, to fit it in our architecture.
>>>>> OP_Column has no intersections with binding machinery.
>>>> 
>>>> Well, I agree something like OP_fetch is necessary.
>> 
>> We can’t we simply do this:

Sorry, I meant:
"Why can’t we simply do this…"

So this is suggestion how to fix redundant fields decoding.

>> Add to ck_constraint array of used field numbers -
>> that’s done during ck_constraint_program_compile()
>> while we have struct Expr by traversing AST. Then,
>> we emit OP_Variable ck_field_count times, where
>> ck_field_count is length of array of used field numbers.
>> 
>> Part of code responsible for CK code generation is:
>> 
>> case TK_COLUMN:{
>>             int iTab = pExpr->iTable;
>>             int col = pExpr->iColumn;
>>             if (iTab < 0) {
>>                    if (pParse->ckBase > 0) {
>>                           /* Generating CHECK constraints. */
>>                           return col + pParse->ckBase;
>>                    }
>> 
>> 
>> So we have to pass that array to parsing context.
>> Using that array code will look like this:
>> 
>> …
>> for (int i = 0; i < ck_field_count; ++i) {
>> 	if (ck_fields[i] == col)
>> 		return ck_fields[i];
>> }
>> assert(0);
>> 
>> When it’s time to run program, we go through array
>> and assign only fields present there:
>> 
>> …
>> for (int i = 0; i < ck_field_count; ++i) {
>> 	sql_bind_decode(&bind, ck_fields[i])
>> 	sql_bind_column(...)
>> }
> 
> I believe I understand how it works now. 
> 
> What is the problem in fixing it? In scope of this patch set or a
> different one is another issue.
> 
> 
> -- 
> Konstantin Osipov, Moscow, Russia, +7 903 626 22 32