Modyfication Sort Merge Join Alghoritm - Mailing list pgsql-hackers

Hi users.
I want to sure, that is no this implementation in Postgresql:
For Sorte Merge Join Alghoritm:
 If the large input arrives sorted,
g-join joins its pages with the buffer pool contents by strictly
increasing join key values and the join output is also strictly
sorted.
 
Is it difficult to implement this functionality?
Best Regards,
Tom