create table test (col1 int, col2 varchar(10), col3 date);
insert into test values (1, 'qwerty', current_date);
alter table test drop col2;
select * from test order by col1 with lock; -- crash here
1) Sorting must be present (in order to set the re-fetch flag)
2) The on-disk record must be in the prior format which must be longer than the current one
In this case deallocated memory is accessed which may lead to either crashing (most probably) or record/index errors.