dblink will run out of o/s memory

 We want to transfer big tables by dblink. But I can't find any memory limitation about dblink in document. We ever experienced that transfering big table by dblink in Posrgresql runs out of our o/s memory.  We want to know if Oracle has any situation like running out of memory and how dblink processes, transfer data rows by rows or table by table?

 Thank you.

          PaoHua