Re: [tarantool-patches] [PATCH v2 2/3] Put all new rows to the end of journal request

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Wed, Mar 06, 2019 at 11:16:17PM +0300, Georgy Kirichenko wrote:
> Form a separate transaction with all local changes in case of replication.
> This is important because we should be able to replicate such changes
> (e.g. made within an on_replace triggers) back. In the opposite case
> local changes will be incorporated into originating transaction and
> wold be skipped by originator replica.
> 
> Needed for: #2798
> ---
>  src/box/txn.c | 36 ++++++++++++++++++++++++++++--------
>  src/box/txn.h |  4 ++++
>  2 files changed, 32 insertions(+), 8 deletions(-)
> 
> diff --git a/src/box/txn.c b/src/box/txn.c
> index 7900fb3ab..187e1c085 100644
> --- a/src/box/txn.c
> +++ b/src/box/txn.c
> @@ -141,6 +141,8 @@ txn_begin(bool is_autocommit)
>  	/* Initialize members explicitly to save time on memset() */
>  	stailq_create(&txn->stmts);
>  	txn->n_rows = 0;
> +	txn->has_rows_with_lsn = false;
> +	txn->has_rows_without_lsn = false;
>  	txn->is_autocommit = is_autocommit;
>  	txn->has_triggers  = false;
>  	txn->is_aborted = false;
> @@ -233,6 +235,8 @@ txn_commit_stmt(struct txn *txn, struct request *request)
>  	if (stmt->space == NULL || !space_is_temporary(stmt->space)) {
>  		if (txn_add_redo(stmt, request) != 0)
>  			goto fail;
> +		txn->has_rows_with_lsn |= stmt->row->replica_id != 0;
> +		txn->has_rows_without_lsn |= stmt->row->replica_id == 0;
>  		++txn->n_rows;
>  	}
>  	/*
> @@ -272,13 +276,29 @@ txn_write_to_wal(struct txn *txn)
>  
>  	struct txn_stmt *stmt;
>  	struct xrow_header **row = req->rows;
> -	stailq_foreach_entry(stmt, &txn->stmts, next) {
> -		if (stmt->row == NULL)
> -			continue; /* A read (e.g. select) request */
> -		*row++ = stmt->row;
> -		req->approx_len += xrow_approx_len(stmt->row);
> +	if (txn->has_rows_with_lsn) {
> +		/* Write out rows that already have an assigned lsn. */
> +		stailq_foreach_entry(stmt, &txn->stmts, next) {
> +			if (stmt->row == NULL)
> +				continue; /* A read (e.g. select) request */
> +			if (stmt->row->replica_id == 0)
> +				continue; /* A row without lsn. */
> +			*row++ = stmt->row;
> +			req->approx_len += xrow_approx_len(stmt->row);
> +		}
> +	}
> +	if (txn->has_rows_without_lsn) {
> +		/* Write out rows to assign a lsn. */
> +		stailq_foreach_entry(stmt, &txn->stmts, next) {
> +			if (stmt->row == NULL)
> +				continue; /* A read (e.g. select) request */
> +			if (stmt->row->replica_id != 0)
> +				continue; /* A row with lsn. */
> +			*row++ = stmt->row;
> +			req->approx_len += xrow_approx_len(stmt->row);
> +		}

I liked the previous approach, where you counted remote rows, much more.
For one thing, it didn't require two passes over the statement list.
I don't understand why you ditched it.

>  	}
> -	assert(row == req->rows + req->n_rows);
> +	assert(row == req->rows + txn->n_rows);
>  
>  	ev_tstamp start = ev_monotonic_now(loop());
>  	int64_t res = journal_write(req);
> @@ -399,8 +419,6 @@ txn_rollback()
>  		txn_stmt_unref_tuples(stmt);
>  
>  	TRASH(txn);
> -	/** Free volatile txn memory. */
> -	fiber_gc();
>  	fiber_set_txn(fiber(), NULL);
>  }
>  
> @@ -480,6 +498,8 @@ box_txn_rollback()
>  		return -1;
>  	}
>  	txn_rollback(); /* doesn't throw */
> +	/** Free volatile txn memory. */
> +	fiber_gc();
>  	return 0;
>  }

As I told you during the previous review session, moving fiber_gc from
txn_rollback to box_txn_rollback is a separate change. In fact, it's a
follow-up for 77fa1736dbb9 ("box: factor fiber_gc out of txn_commit").
Please submit it in a separate patch with a proper commentary.