Oracle XML functions with large datasets

Oracle XML functions with large datasets

I have problems to use the Oracle XML functions like
xmlelement, xmlagg, xmlattributes
For instance:
select
XMLELEMENT(
"OrdrList",
XMLAGG(
XMLELEMENT(
"IDs",
XMLATTRIBUTES(
USERCODE AS "usrCode",
VALDATE AS "validityDate"
)
)
)
) from TMP
/
The code seems to be correct as it does work when returning a small number
of messages
And yes, I did try to set "long", "pagesize", "linesize" etc... but have
never been able to retrieve the full set of approx. 500.000 XML-messages
(i.e. table rows).
Reading some background literature (e.g. "Oracle SQL" by Jürgen Sieben) it
seems that the functions are not designed for large data sets. Mr. Sieben
explains that he uses these only for small queries (max. 1 MB output
size), above that he recommends to use "object-oriented functions" but
does not explain which.
Does somebody have experience with this and has the above XML-functions
working or knows alternatives?