A coworker at GitHub found a few months back that if we used
`santitize_sql` over `where` when we knew the values going into `where`
it was a lot faster than `where`.
This PR adds a new Arel node type called `HomogenousIn` that will be
used when Rails knows the values are all homogenous and can therefore
pick a faster codepath. This new codepath skips some of the required
processing by `where` to make `wheres` with homogenous arrays faster
without requiring the application author to know when to use which query
type.
Using our benchmark code:
```ruby
ids = (1..1000).each.map do |n|
Post.create!.id
end
Benchmark.ips do |x|
x.report("where with ids") do
Post.where(id: ids).to_a
end
x.report("where with sanitize") do
Post.where(ActiveRecord::Base.sanitize_sql(["id IN (?)", ids])).to_a
end
x.compare!
end
```
Before this PR comparing where with a list of IDs to santitize sql:
```
Warming up --------------------------------------
where with ids 11.000 i/100ms
where with sanitize 17.000 i/100ms
Calculating -------------------------------------
where with ids 115.733 (± 4.3%) i/s - 583.000 in 5.045828s
where with sanitize 174.231 (± 4.0%) i/s - 884.000 in 5.081495s
Comparison:
where with sanitize: 174.2 i/s
where with ids: 115.7 i/s - 1.51x slower
```
After this PR comparing where with a list of IDs to santitize sql:
```
Warming up --------------------------------------
where with ids 16.000 i/100ms
where with sanitize 19.000 i/100ms
Calculating -------------------------------------
where with ids 158.293 (± 6.3%) i/s - 800.000 in 5.072208s
where with sanitize 169.141 (± 3.5%) i/s - 855.000 in 5.060878s
Comparison:
where with sanitize: 169.1 i/s
where with ids: 158.3 i/s - same-ish: difference falls within error
```
Co-authored-by: Aaron Patterson <aaron.patterson@gmail.com>
