Re: On disable_cost

On Fri, 27 Sept 2024 at 20:42, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> wrote:
> 2. The "disabled nodes" are not only shown at the nodes where nodes
> were actually disabled, but also at every nodes above these nodes.

I'm also not a fan either and I'd like to see this output improved.

It seems like it's easy enough to implement some logic to detect when
a given node is disabled just by checking if the disable_nodes count
is higher than the sum of the disabled_node field of the node's
children. If there are no children (a scan node) and disabed_nodes >
0 then it must be disabled. There's even a nice fast path where we
don't need to check the children if disabled_nodes == 0.

Here's a POC grade patch of how I'd rather see it looking.

I opted to have a boolean field as I didn't see any need for an
integer count. I also changed things around so we always display the
boolean property in non-text EXPLAIN. Normally, we don't mind being
more verbose there.

I also fixed a bug in make_sort() where disabled_nodes isn't being set
properly. I'll do an independent patch for that if this goes nowhere.

David