Reduce size of Expr struct

[alamb]

Is your feature request related to a problem or challenge?

For unrelated reasons, I reduced the size of Expr from 272 to 112 bytes in this PR:

• Reduce size of Expr struct #14366

It turns out this change resulted in a a pretty significant (10-20% faster) improvement in planning time #14366 (comment):

group                                         alamb_make_expr_smaller                main
-----                                         -----------------------                ----
physical_plan_clickbench_all                  1.00    285.4±4.98ms        ? ?/sec    1.14    324.2±6.52ms        ? ?/sec
physical_plan_clickbench_q1                   1.00      4.6±0.12ms        ? ?/sec    1.10      5.0±0.13ms        ? ?/sec
physical_plan_clickbench_q10                  1.00      5.7±0.14ms        ? ?/sec    1.16      6.5±0.42ms        ? ?/sec
physical_plan_clickbench_q11                  1.00      5.8±0.22ms        ? ?/sec    1.13      6.6±0.21ms        ? ?/sec
physical_plan_clickbench_q12                  1.00      6.0±0.17ms        ? ?/sec    1.12      6.7±0.24ms        ? ?/sec
physical_plan_clickbench_q13                  1.00      5.5±0.11ms        ? ?/sec    1.12      6.1±0.17ms        ? ?/sec
physical_plan_clickbench_q14                  1.00      5.8±0.17ms        ? ?/sec    1.12      6.5±0.15ms        ? ?/sec
physical_plan_clickbench_q15                  1.00      5.6±0.14ms        ? ?/sec    1.13      6.3±0.18ms        ? ?/sec
physical_plan_clickbench_q16                  1.00      5.1±0.18ms        ? ?/sec    1.09      5.5±0.19ms        ? ?/sec
physical_plan_clickbench_q17                  1.00      5.0±0.13ms        ? ?/sec    1.14      5.8±0.15ms        ? ?/sec
physical_plan_clickbench_q18                  1.00      4.9±0.13ms        ? ?/sec    1.12      5.4±0.15ms        ? ?/sec
...

Describe the solution you'd like

I would like to make a new PR that reduces the size of Expr

Describe alternatives you've considered

I suggest

1. Change Expr::WindowFunction(WindowFunction) --> Expr::WindowFunction(Box<WindowFunction>) as described on Reduce size of Expr struct #14366
2. Add a regression test for Expr size to ensure we don't get a regression again

Additional context

I recommend:

1. Updating the Expr::WindowFunction definition
2. Letting the compiler guide you to code that needs to be updated and follow the pattern from Reduce size of Expr struct #14366
3. Copy the tests from Reduce size of Expr struct #14366

[alamb]

I think this is a good first issue because

1. there is an example / pattern to follow
2. There is evidence that this will make significant improvements

[hendrikmakait]

take

[alamb]

Thanks @hendrikmakait !

[Omega359]

I am surprised by the magnitude of the performance uptick by essentially moving something from the stack to the heap.

[alamb]

I am surprised by the magnitude of the performance uptick by essentially moving something from the stack to the heap.

My theory is that the performance difference is not the move to the heap but the fact that then all the places that make Exprs and copy them, etc have less work to do (as the Expr struct is half the size)

[Omega359]

🤔