bi publisher report can generate in OBIEE analytics in less 5 mins, but cannot generate in xmlpserve

I have a embedded bi publisher report that can be generate in OBIEE 10.1.3.4.2 analytics in less than 5 mins, but cannot generate in xmlpserver.
It complains of java out of memory error. So we increase the size to 1024mb for JVM
But don't seems to be enough.
Can someone explain why in analytics it has no issue opening but when in xmlpserver (BI publisher enterprise 10.1.3.4.2) it has problem opening it? Is this normal?

I mean why analytics side do not need as much memory as the xmlpserver?

Thanks in advance for any advice.