[tarantool-patches] Re: [PATCH v3 4/7] iproto: replace obuf by mpstream in execute.c

[Vladislav Shpilevoy]

On 30/11/2018 13:19, Vladimir Davydov wrote:
> On Thu, Nov 29, 2018 at 05:04:06PM +0300, Vladislav Shpilevoy wrote:
>> On 29/11/2018 13:53, Vladimir Davydov wrote:
>>> On Tue, Nov 27, 2018 at 10:25:43PM +0300, imeevma at tarantool.org wrote:
>>>> @@ -627,81 +610,53 @@ sql_prepare_and_execute(const struct sql_request *request,
>>>>    }
>>>>    int
>>>> -sql_response_dump(struct sql_response *response, int *keys, struct obuf *out)
>>>> +sql_response_dump(struct sql_response *response, int *keys,
>>>> +		  struct mpstream *stream)
>>>>    {
>>>>    	sqlite3 *db = sql_get();
>>>>    	struct sqlite3_stmt *stmt = (struct sqlite3_stmt *) response->prep_stmt;
>>>> -	struct port_tuple *port_tuple = (struct port_tuple *) &response->port;
>>>>    	int rc = 0, column_count = sqlite3_column_count(stmt);
>>>>    	if (column_count > 0) {
>>>> -		if (sql_get_description(stmt, out, column_count) != 0) {
>>>> +		if (sql_get_description(stmt, stream, column_count) != 0) {
>>>>    err:
>>>>    			rc = -1;
>>>>    			goto finish;
>>>>    		}
>>>>    		*keys = 2;
>>>> -		int size = mp_sizeof_uint(IPROTO_DATA) +
>>>> -			   mp_sizeof_array(port_tuple->size);
>>>> -		char *pos = (char *) obuf_alloc(out, size);
>>>> -		if (pos == NULL) {
>>>> -			diag_set(OutOfMemory, size, "obuf_alloc", "pos");
>>>> -			goto err;
>>>> -		}
>>>> -		pos = mp_encode_uint(pos, IPROTO_DATA);
>>>> -		pos = mp_encode_array(pos, port_tuple->size);
>>>> -		/*
>>>> -		 * Just like SELECT, SQL uses output format compatible
>>>> -		 * with Tarantool 1.6
>>>> -		 */
>>>> -		if (port_dump_msgpack_16(&response->port, out) < 0) {
>>>> +		mpstream_encode_uint(stream, IPROTO_DATA);
>>>> +		mpstream_flush(stream);
>>>> +		if (port_dump_msgpack(&response->port, stream->ctx) < 0) {
>>>
>>> stream->ctx isn't guaranteed to be an obuf
>>>
>>> And when you introduce vstream later, you simply move this code to
>>> another file. This is confusing. May be we should pass alloc/reserve
>>> used in mpstream to port_dump instead of obuf?
>>
>> Good idea, though not sure, if it is worth slowing down port_dump_msgpack
>> adding a new level of indirection. Since port_dump_msgpack is a hot path
>> and is used for box.select.
>>
>> Maybe it is better to just rename port_dump_msgpack to port_dump_obuf
>> and rename vstream_port_dump to vstream_port_dump_obuf? If we ever will
>> dump port to not obuf, then we will just add a new method to port_vtab.
>>
>> Also, it would make port_dump_obuf name consistent with port_dump_lua -
>> in both cases we not just dump in a specific format, but to a concrete
>> destination: obuf and lua stack. Now port_dump_msgpack anyway is restricted
>> by obuf destination.
> 
> There's port_dump_plain, which dumps port contents in a specific format.
> So port_dump_obuf would look ambiguous.
> 
>>
>> If you worry about how to call sql_response_dump() to not obuf, then there
>> is another option. Anyway rename port_dump_msgpack to port_dump_obuf and
>> introduce a new method: port_dump_mpstream. It will take mpstream and use
>> its reserve/alloc/error functions. It allows us to do not slow down box.select,
>> but use the full power of virtual functions in execute.c, which definitely is
>> not hot.
> 
> That would interconnect port and mpstream, make them dependent on each
> other. I don't think that would be good.
> 
>>
>> mpstream implementation of vstream will call port_dump_mpstream, and
>> luastream implementation of vstream will call port_dump_lua as it does now.
>> box.select and iproto_call will use port_dump_obuf.
>>
>> I prefer the second option: introduce port_dump_mpstream. It is ok for you?
> 
> I may be wrong, but IMO there isn't much point in optimizing box.select,
> because it's very limited in its applicability. People already prefer to
> use box.call over box.insert/select/etc over iproto, and with the
> appearance of box.execute they are likely to stop using plain box.select
> at all.
> 
> That said, personally I would try to pass reserve/alloc methods to port,
> see how it goes.
> 

I do not see a reason to slow down box.select if we can don't do it.
Yeas, people use IPROTO_CALL, but in stored functions they use box
functions including select.

Ok, instead of port_dump_mpstream we can rename port_dump_msgpack to
port_dump_obuf and add port_dump_msgpack which does not depend on
mpstream and takes alloc/reserve/ctx directly.