On 23.08.24 10:27, Richard Guo wrote:
On Fri, Aug 23, 2024 at 11:56 AM Tom Lane <t...@sss.pgh.pa.us> wrote:
Richard Guo <guofengli...@gmail.com> writes:
I agree that it’s always desirable to postpone work from path-creation
time to plan-creation time. In this case, however, it’s a little
different. The projection step could actually be avoided from the
start if we perform the correct check in create_ordered_paths.
Well, the question is how expensive is the "correct check" compared
to what we're doing now. It might be cheaper than creating an extra
level of path node, or it might not. An important factor here is
that we'd pay the extra cost of a more complex check every time,
whether it avoids creation of an extra path node or not.
Fair point. After looking at the code for a while, I believe it is
sufficient to compare PathTarget.exprs after we've checked that the
two targets have different pointers.
- if (sorted_path->pathtarget != target)
+ if (sorted_path->pathtarget != target &&
+ !equal(sorted_path->pathtarget->exprs, target->exprs))
sorted_path = apply_projection_to_path(root,
ordered_rel,
equal() already checks whether both pointers are equal, so I think this
could be simplified to just
if (!equal(sorted_path->pathtarget->exprs, target->exprs))
