[patches] [PATCH] Don't try to lock a ddl latch in a multistatement tx

[Vladimir Davydov]

On Thu, Mar 01, 2018 at 05:12:40PM +0300, Georgy Kirichenko wrote:
> Any ddl is prohibited in a multistatement transaction, there is no
> reason to try to lock a ddl latch in tis case. Locking for already
> locked latch will cause an yield and a silent transaction rollback, and
> this will crash or assert tarantool server.
> 
> Fixes #2783

> diff --git a/src/box/alter.cc b/src/box/alter.cc
> index 5749740d2..b94cf710b 100644
> --- a/src/box/alter.cc
> +++ b/src/box/alter.cc
> @@ -3133,6 +3133,13 @@ lock_before_dd(struct trigger *trigger, void *event)
>  	if (fiber() == latch_owner(&schema_lock))
>  		return;
>  	struct txn *txn = (struct txn *)event;
> +	/*
> +	 * The trigger is executed before any check and may yield but
> +	 * an yield in a non-autocommit memtx transaction will rollback it.
> +	 * So we shouldn't to try to lock a latch if there is a multistatement
> +	 * transaction.
> +	 */
> +	txn_check_singlestatement_xc(txn, "DDL");

This check will raise even if the transaction has no statements at all
so the following code will fail:

  box.begin()
  box.schema.space.create('test')
  box.commit()

AFAIK this will break our SQL implementation.