Sort by date field = outofmemory?

[Bruno Mannina]

Dear Solr Users,

Each time I try to do a request with &sort=pubdate+desc....
I get:
GRAVE: java.lang.OutOfMemoryError: Java heap space

I use Solr3.6, I have around 80M docs and my request gets around 160 
results.

Actually for my test, i use jetty

java -jar -Xmx2g start.jar

PS: If I write 3g i get an error, I have 8go Ram

Thanks a lot for your help,
Bruno