How to create a cursor that is independent of transactions and doesn't calculated when created ?

I wonder how quick is cursor without hold.
I have a data set with 10^7 rows.

*begin;
declare mycursor cursor for select * from z;
commit;
* - this takes 3 ms.

*begin;
declare mycursor cursor with hold for select * from z;
commit;
* - this takes 3 s.

Thus, holdable cursor is getting calculated, obviously.
I cannot use cursor without hold as it requires a connection per query +
client.
But I also don't understand - why cursor with hold should start so much
longer than cursor without hold.

If there any possiblity to have a cursor that as fast as cursor without hold
and as transaction-independent as cursor with hold ?



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