Distributed transaction error ORA-02049: time-out: distributed transaction waiting for lock

Problem

While working with dblinks, I got the below error:

ORA-02049: time-out: distributed transaction waiting for lock

 

Cause

More than one session is accessing the remote object.

 

Solution

I had issued commit, rollback for one of the session and the issue is resolved.

But, the key thing here is that; I could only reproduce the error while issueing below statement:

insert /*+ APPEND PARALLEL(4)*/ into admin.test2 
select /*+ DRIVING_SITE(T) PARALLEL(4) */ * from admin1.test2@MYDB2.WORLD T where 1=1
;

While trying it without APPEND hint it does not occur.

Honestly speaking, I did not know the real cause, because sometimes I could not reproduce the error.

The transactions  are not listed in:

select * from dba_2pc_pending; 

select * from dba_2pc_neighbors;