Use Arc<str> inside Field (#3955)

[tustvold]

Draft as I am not sure about this and needs some shenanigans to work for serde

Which issue does this PR close?

Part of #3955

Rationale for this change

Allows for cheaper cloning of DataType and potentially faster comparisons, by comparing pointers instead of string contents

What changes are included in this PR?

Are there any user-facing changes?

[alamb]

I think if we Arc the entire Field -- as in #3965 we may not need this

I know that @crepererum has mentioned other downstream places that copy the field name (like Statistics in DataFusion) but I think maybe a better design would be to update those downstream uses to hold a FieldRef rather than just the name 🤔

[tustvold]

Agreed, my plan is to see what return we get from #3965 and then revisit this

[crepererum]

hold a FieldRef rather than just the name

That's not always possible, since you may not have the datatype at hand yet. So at least during logical planning in DF this ain't an option.

[alamb]

That's not always possible, since you may not have the datatype at hand yet. So at least during logical planning in DF this ain't an option.

🤔 I think as soon as DataFusion creates a LogicalPlan / Expr it is possible to get the type using https://docs.rs/datafusion/latest/datafusion/prelude/enum.Expr.html#impl-ExprSchemable-for-Expr

Or more to the point, with a LogicalPlan you also have a Schema with Field

[tustvold]

Going to close this for now to clear up the review backlog slightly