Re: explain plan difference

Ravi Krishna <srkrishna@yahoo.com> writes:
>> VACUUM would not change the state of the dropped columns.

> When does it change?

Never, unless you drop and recreate the table.  Removing a dropped
column would change the attnums of following columns, which we
can't support because the tableoid+attnum is the only persistent
identifier of a column.

(From memory, operations like VACUUM FULL and CLUSTER will rewrite
dropped columns with NULLs to reduce their storage impact.  But they
don't go away.)

            regards, tom lane