why do we need create tuplestore for each fetch?

Hi everyone,

I found this several days ago when I try to debug a "fetch" of cursor.
And I have sent a mail to this list, but no one reply...
Maybe this is a very simple problem, please help me, thanks a lot...

Here is the example:
create table t (a int);
insert into t values (1),(3),(5),(7),(9);
insert into t select a+1 from t;
begin;
declare c cursor for select * from t order by a;
fetch 3 in c;
fetch 3 in c;
fetch 3 in c;

In 'PortalRun', a fetch stmt will be treated with PORTAL_UTIL_SELECT,
and then a tuplestore will be created in 'FillPortalStore' in the
fetch stmt's portal.

In 'FillPortalStore', all result will be store at that tuplestore,
Then, go back to 'PortalRun'; next, 'PortalRunSelect' will send this
results to client...

My problem is: why do we need create that tuplestore as an
middle storeage? why do not we just send these result to clent
at the first time?

Thank you very much.

--
GaoZengqi
pgf00a(at)gmail(dot)com
zengqigao(at)gmail(dot)com