Error: DDL statement interfered with this statement

It is very likely there is another DDL statement running in parallel in another session. I have seen this type of error message myself when I was loading data in schema A while trying to drop a table in schema B. The catalog object in Vertica seems to be Global in scope. And DDL operations can easily lock each other out.

What version of vertica are you running? If it's V4.x, there was a bug and  resolved in 5.0 patch set.

In my case, I was running 6.1.x when I saw a message very much like in the OP (I don't remember whether it was from [VJDBC] or not). I was running a background (nohup) batch job that does bulk-load then bulk-insert:
copy A ... from local file;
copy B ... from local file;
insert into C 
select .. from A ;
insert into C
select ... from B;

There were dozen such statements in all, each takes at least minutes to complete. While running the script I realized that the disk space was below the 50% mark so I started another process to drop schemas: drop schema Y1 cascade;

Later I found out some tables in the loading job didn't get populated and went back to see the logs. That is when I saw the error message (from the loading script).

For various reasons I didn't create a support ticket (e.g. not a production instance, time-consuming to reproduce, etc.) Are you sure this issue was fixed in 5.0 and on ward?