[PATCH 4/6] txn: do not require space id for nop requests

[Konstantin Osipov]

* Vladimir Davydov <vdavydov.dev at gmail.com> [18/06/13 20:40]:
> Currently, IPROTO_NOP can only be generated by a before_replace trigger,
> when it returns the old tuple thus turning the original operation into a
> NOP. In such a case we know the space id and we write it to the request
> body. This allows us to dispatch NOP requests via DML route.
> 
> As a part of replica local spaces feature, we will substitute requests
> operating on local spaces with NOP in relay in order to promote vclock
> on replicas without actual data modification. Since space_id is stored
> in request body, sending it to replicas would mean decoding the request
> body in relay, which is an overkill. To avoid that, let's separate NOP
> and DML paths and remove space_id from NOP requests.

LGTM, a few comments below.

> @@ -277,6 +277,11 @@ apply_row(struct xstream *stream, struct xrow_header *row)
>  	(void) stream;
>  	struct request request;
>  	xrow_decode_dml_xc(row, &request, dml_request_key_map(row->type));
> +	if (request.type == IPROTO_NOP) {
> +		if (txn_commit_nop(&request) != 0)
> +			diag_raise();
> +		return;
> +	}

txn_commit_nop() -> box_process_nop() or process_nop().

> @@ -50,7 +50,6 @@ request_create_from_tuple(struct request *request, struct space *space,
>  			  struct tuple *old_tuple, struct tuple *new_tuple)
>  {
>  	memset(request, 0, sizeof(*request));
> -	request->space_id = space->def->id;
>  
>  	if (old_tuple == new_tuple) {
>  		/*
> @@ -61,6 +60,7 @@ request_create_from_tuple(struct request *request, struct space *space,
>  		return 0;
>  	}
>  
> +	request->space_id = space->def->id;

Please add a comment 
   /*
    * Space pointer may be zero in case of NOP, in which case this
    * line is not reached.
    */


You changed a lot of code making it more NOP friendly, for example 
txn_begin_in_engine() now works even if there is already a
transaction which has a NOP statement. This seems like a bug fix
with no test. Could you please add a test?

-- 
Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov