Parallel Query In PostgreSQL Robert Haas

I and others have been working on bringing parallel query for PostgreSQL for several years now, but PostgreSQL 9.6 is the first release expected to include a user-visible feature. And it's pretty cool. In this talk, I'll give an overview of the development of this feature, where we are now, and what the future might hold. I will discuss the overall architecture of parallelism in PostgreSQL, give examples of queries that can be accelerated by the features expected to be in PostgreSQL 9.6, and talk about what's not done yet.

[CAUTHAYAKUMAR]

I created a Function default set as parallel unsafe (the function contain only select queries).For sometimes the function return nothing on that after some attempts the function return data.This was the cause because of parallel unsafe?