postgresql max memory (pl/Perl)

hi

in my application i select data from my database and i store it into a
pl/perl variable $myClob.

the quantity of data is very big (around 250Mo, growing to 800Mo). and next
i write this data into a file.
with Oracle, it works, but with Oracle i get an exception saying that
postgresql use a memory adress which is not allowed (or not in write mode).

my database is install on windows2000NT, with PIV 2.8Ghz and 1Go RAM.
does this error comes from the configuration of my database, the limits of
postgresql, or does i must write the file in several times ?

an other question is that the application will run on others plateform :
does i will get an error with a SUN station : biprocessor, 4Go RAM and
solaris 2.8 ?

regards

Will