Randall Lucas <rlucas@tercent.com> writes:
> I am holding hierarchical data in a table and often need to calculate the "root" of a hierarchy. Initially,
> a recursive plpgsql function worked just fine. But performance started to lag when I got to scale.
>
> So, I added a functional index.
>
> create table example (id serial primary key, stuff text, parent_id int);
> create index example_root_idx on example (get_root_id(id));
>
> (get_root_id(id) pulls an example row and recurses onto parent_id until it hits a root)
>
> This works fine for speeding up access to the existing data, but breaks for inserting new rows because
> get_root_id(id) can't find the new row. It looks like the index is getting calculated, and the function
> called, before the row becomes visible to the function.
Change your get_root_id(id) into get_root_id(example), after this you can start
searching for root not from current id but from it parent_id. Parent is already
exist in table. If parent_id is null - it is root and get_root_id(example) do
not need scan table and will return example.id from it input argument.
--
Sergey Burladyan
