Flink Cross Strategies

[gen-too]

Hi,

I would like to knot how the Flink cross function works. I found that 
there are four strategies ( NESTEDLOOP_BLOCKED_OUTER_FIRST, 
NESTEDLOOP_BLOCKED_OUTER_SECOND, NESTEDLOOP_STREAMED_OUTER_FIRST, 
NESTEDLOOP_STREAMED_OUTER_SECOND), but I need some more detailed 
explanations please.

Thanks