Plsql Function with error: No space left on device.

HAllo!

I have wrote a function. If I call this function the following output
appears:

psql:restructure.sql:139: ERROR:  cannot extend image: No space left on
device.
        Check free disk space.

My Postgres version is 7.1.2
My Server has the following data:


Main memory size: 510 Mbytes
1 GenuineIntel Pentium III (Coppermine) processor
1 vga+ graphics device
1 keyboard
1 parallel port:
  lp0: base 0x378, no irq, no dma, modes SPP,ECP,ECPEPP,ECPPS2
PCI bus devices:
    Host bridge: Intel 440BX - 82443BX Host (rev 3).
    PCI bridge: Intel 440BX - 82443BX AGP (rev 3).
    ISA bridge: Intel 82371AB PIIX4 ISA (rev 2).
    IDE interface: Intel 82371AB PIIX4 IDE (rev 1).
    USB Controller: Intel 82371AB PIIX4 USB (rev 1).
    Bridge: Intel 82371AB PIIX4 ACPI (rev 2).
    SCSI storage controller: Adaptec AIC-7890/1 (rev 0).
    PCI bridge: DEC DC21152 (rev 3).
    Ethernet controller: Intel 82557 (rev 8).
    Multimedia audio controller: Ensoniq ES1371 (rev 8).
    Multimedia video controller: Zoran ZR36057 (rev 2).
    VGA compatible controller: Matrox Matrox G200 AGP (rev 3).
    Display controller: Matrox Matrox G200 AGP (rev 3).


This is the function:
CREATE FUNCTION series_image () RETURNS integer AS '
        DECLARE

                psr_rec record;
                i integer := 0;

BEGIN
        FOR psr_rec IN SELECT * FROM relseries_image000 LOOP
                UPDATE image
                        SET seriesoid  = psr_rec.parentoid
                        WHERE chilioid = psr_rec.childoid;
                i := i + 1;
        END LOOP;
        IF NOT FOUND THEN RETURN -1;
                ELSE RETURN i;
        END IF;
END;

' LANGUAGE 'plpgsql';



I saw during the execute of the function that the Ram was fully used and
also the swap space was also fully used.

How could I optimize the function above with new constructs of 7.1?

the table relseries_image000 has ca. 3 Millions of rows. Every row has 3
columns.

Thank you in advance for your help

David