[tarantool-patches] Re: [PATCH v3 0/3] box: run checks on insertions in LUA spaces

[n.pettik]

>> On 14 May 2019, at 20:00, Konstantin Osipov <kostja at tarantool.org> wrote:
>> 
>> * Kirill Shcherbatov <kshcherbatov at 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:

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(...)
}

>>> Fire CK constraints for LUA spaces.
>>> To achieve this goal, we reworked data dictionary, to store ck
>>> constraints in separate space _ck_constraints and updated data
>>> migration script to migrate existent data there. This also would
>>> be useful in future to implement ALTER SPACE ADD CONSTRAINT
>>> operation. Now we do not support CK constraint creation on
>>> non-empty space.
>> 
>> Is there a ticket for adding CHECK constraint on a non-empty
>> space?
>> 
>> We need to add a general do-any-alter-by-rebuild algorithm so that
>> all such features work by rebuilding a table. We could optimize
>> these later.
>> 
>> *No* SQL feature is usable unless DDL related to this feature
>> works on a non-empty space, at least somehow.
>> 
>>> Each CK has own precompiled VDBE machine that performs this
>>> check with tuple fields mapped to it's memory with sql_bind() api.
>> 
>> Good.
>> 
>> 
>> -- 
>> Konstantin Osipov, Moscow, Russia, +7 903 626 22 32

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