What is the metadata field in DataSchema used for?

[RinChanNOWWW]

https://github.com/datafuselabs/databend/blob/93621e902bd172cb4fd60fab4a90d927b6e3d2be/common/datavalues/src/data_schema.rs#L26-L31

I'm implementing comments for columns now. I find that there is a metadata field in DataSchema, and I'm wondering if I should put the comment in metadata or in DataField.

[BohuTANG]

Has not seen anywhere to use it, I think @youngsofun may know more about it.

[youngsofun]

@RinChanNOWWW it`s explained here https://databend.rs/doc/contributing/rfcs/new-sql-planner-framework#binder

[RinChanNOWWW]

It seems that the metadata in binder is not the same with the one in DataSchema. And DataSchema.metadata is never written.

[youngsofun]

sorry, I was busy and misread your question.

it is corrisponding to metadata of Arrow schema.
not sure whether it will be used later

but itself looks more like a table level metadata, (not field level).

and I think we can just store column comments in tableInfos in catelog . don`t need to carry it in Schema.

[sundy-li]

Metadata will be used to convert into Arrow's schema. See: https://github.com/jorgecarleitao/arrow2/blob/main/src/datatypes/schema.rs#L13-L29

[RinChanNOWWW]

So it's just for keeping same with Arrow?

[sundy-li]

Yes