processing large amount of rows with plpgsql

hello everybody,

we are trying to move the data from table1 into table2 using a plpgsql stored procedure which is performing simple a
dataconversion 

there are about 50 million rows

the tables are relatively simple, less than a dozen columns, most are integer, a couple are char(32) and one is varchar
holdingURLs 

what happens is that when we execute the stored procedure, the execution eats up the 17 GB free space on the server and
theserver crashes 

if we apply a limit of 1 million rows, the execution completes successfully in about a minute

we understand, by now, that plpgsql functions are executed in their own transaction, which commits when the function
comesto an end 

the question is -

are plpgsql functions suitable for such massive operations on data and can this work without so much disk space is
beingeaten for something which should be simply "read-change-write, read-change-write, read-change-write, …"? i. e. any
wayto force commit inside, or so? 

or should we rather implement this operation in some external scripting language (speed is not that important, this is
aone time conversion) 

thank you,
geert