my ho <mthoatbanjo@yahoo.com> writes:
> If anyone can help pls, I have a question abt the
> execution of cursor create/fetch/move , in particular
> about disk cost. When a cursor is created, is the
> whole table (with the required columns) got put into
> memory?
No. The plan is set up and then incrementally executed each time you
say FETCH.
> how does postgre speed up the query in
> compare to normal selection?
The only difference from a SELECT is that the planner will prefer
"fast-start" plans, on the theory that you may not be intending
to retrieve the whole result. For instance it might prefer an
indexscan to a seqscan + sort, when it otherwise wouldn't.
regards, tom lane