Sequences - problem

Hallo!

I created several tables using a id-sequence for each:
create sequence portid;
create table ports(id integer primary key default nextval('portid'), name
varchar);

Now, since it is a web-application I am working on, I have several
Perl-scripts acting on/with the database.

THe informations-program simply has to read out each sequence in order to
give some statistical data about the database (number of ports, people
...)

As I try a
Pg::doQuery("select currval('portid');", \@ports);
the program gets no reply, on the Postmaster-task (I did not get
postmaster start on startup/background, runs on a task in foreground) I
that message:
ERROR:  regionid.currval is not yet defined in this session
ERROR:  jpid.currval is not yet defined in this session
ERROR:  countri.currval is not yet defined in this session
ERROR:  jprid.currval is not yet defined in this session
ERROR:  portid.currval is not yet defined in this session


What does the problem consist in, and how can I solve it?

In my opinion it is better to read out the counter instead of querying all
elements in a table, so to get the number of elements ...
Pg::doQuery("select * from ports;", \@ports);
Where the number I am looking for is $#ports then ...

I think this method will take a lot of time and is not very effective, as
I do not think I wil ever access one of the entrys read (at least not
while putting some information) ...


Saluti!

Ludwig