PGA settings

Hi Gurus,

Please help me in understanding the following.... 

I have 8 GB of RAM for Oracle on Solaris. 

At instance level the following parameters are set: 
SGA_MAX_SIZE=4GB 
PGA_AGGREGATE_TARGET=2GB 
WORK_AREA_SIZE_POLICY=AUTO 

At session level I have set the following: 
WORK_AREA_SIZE_POLICY=MANUAL 
HASH_AREA_SIZE=2GB 

Now my questions are: 

1> What is the Maximum memory that can be used by Oracle at any point in time? 
Is it 6GB (4+2)? 

2> If the answer to the above question is yes, then will the HASH_AREA_SIZE 
mentioned at the session level be allocated from PGA_AGGREGATE_TARGET memory? 

3> What will be the SORT_AREA_SIZE value for the said session? 

4> If parallel queries are run from that session, will each PQ process have 2GB 
of RAM for HASH_AREA_SIZE? 

Regards,

Deep

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