Hi,
> The check for parallel_safe should be even cheaper than cost comparison
> so I think it's better to do that first. The attached patch does this
> and also updates the comment to mention the requirement about being
> parallel-safe.
The patch was marked as "Needs review" so I decided to take a look.
I see the reasoning behind the proposed change, but I'm not convinced
that there will be any measurable performance improvements. Firstly,
compare_path_costs() is rather cheap. Secondly, require_parallel_safe
is `false` in most of the cases. Last but not least, one should prove
that this particular place is a bottleneck under given loads. I doubt
it is. Most of the time it's a network, disk I/O or locks.
So unless the author can provide benchmarks that show measurable
benefits of the change I suggest rejecting it.
--
Best regards,
Aleksander Alekseev
