Re: Parallel hints in PostgreSQL with consistent perfromance

On Thu, Dec 28, 2023 at 7:47 AM mohini mane <mohini(dot)android(at)gmail(dot)com>
wrote:

> Thank you for your response !!
> I am experimenting with SQL query performance for SELECT queries on large
> tables and I observed that changing/increasing the degree of parallel hint
> doesn't give the expected performance improvement.
>

But you still have addressed the fact that PostgreSQL *does not have
planner hints*.

Are you using some nonstandard extension, or nonstandard fork?

> I have executed the SELECT query with 2,4 & 6 parallel degree however
> every time only 4 workers launched & there was a slight increase in
> Execution time as well,
>

Adding an ignored comment to your SQL would not be expected to do
anything. So it is not surprising that it does not do anything about
the number of workers launched. It is just a comment. A note to the human
who is reading the code.

> why there is an increase in execution time with parallel degree 6 as
> compared to 2 or 4?
>

Those small changes seem to be perfectly compatible with random noise. You
would need to repeat them dozens of times in random order, and then do a
statistical test to convince me otherwise.

>