ORA-04030 means machine hosting database instance has run out of memory because database instance is requesting memory for PGA.

In some cases allocated PGA can exceed PGA_AGGREGATE_TARGET parameter because untunable PGA may grow very large due to PL/SQL collections variables for example.

You can check maximum PGA allocated in GB with:

SQL> select name, value/(1024*1024*1024) GB from v$pgastat where name like '%max
%allocated%';

NAME                                                                     GB
---------------------------------------------------------------- ----------
maximum PGA allocated                                            ,080384254

Note: Thanks to Forstmann, the above was originally published at http://forums.oracle.com/forums/thread.jspa?threadID=1120120&tstart=15. I published above from my old notes but the reference was missing from there.