DDL statement blocked on long-running query with no runtime dependancy

[Tim Kane <tim.kane@xxxxxxxxx>]

Hi all,

I’ve just noticed that some DDL statements will block if there are other queries accessing the relation in question, even where those queries are not dependant on the underlying structures (such as a new index, created after the initial query).

For instance…

SELECT long_running_query FROM foo;   -- Query A,

--   meanwhile…

CREATE UNIQUE INDEX ON foo USING btree (blah);

-- Fine, no problem

DROP INDEX foo_blah_idx;  

-- The above DDL statement will block until Query A completes, even though the query cannot possibly rely on the newly created index

Is this behaviour by design? Is it worth allowing DDL statements to occur where it can be determined that no currently running query will be affected?

Cheers,

Tim