Schema Browser message shows, "A query is executing in single-thread mode" when sorting on a column (4270492)

When running the following:

BEGIN
DBMS_LOCK.sleep(seconds => 1000.01);
END;
/

It runs a long running query and takes several minutes to return all records.

In that time, if you go to the Schema Browser, find the table that is being queried and click on the Data tab.

On the right hand side, if you do a column search on a Primary Key, Toad shows the following message:

'A query is executing in single-thread mode'

If you have the "Execute Multiple threads" option checked, it still won’t allow it.

Wait until the query in the Editor is done running before doing the column search in the Schema Browser.