Help to review the with X cursor option.

The cursor means something like declare c cursor for select * from t;
The holdable cursor means declare c cursor WITH HOLD for select * from t;

Holdable cursor is good at transaction, user can still access it after the
transaction is commit. But it is bad at it have to save all the record to
tuple store before we fetch 1 row.

what I want is:
1. The cursor is still be able to fetch after the transaction is
committed.
2. the cursor will not fetch the data when fetch statement is issue (just
like non-holdable cursor).

I called this as with X cursor..

I check the current implementation and think it would be possible with the
following methods:
1. allocate the memory in a {LongerMemoryContext}, like EState to
prevent they are
2. allocate a more bigger resource owner to prevent the LockReleaseAll
during CommitTransaction.
3. add the "with X" option to cursor so that Precommit_portals will not
drop it during CommitTransaction.

Before I implement it, could you give some suggestions?

Thanks!