Disambiguatation of existing schemas.

[v0y4g3r]

What type of enhancement is this?

Other

What does the enhancement do?

Looks like there are too many "schemas" in project:

• ColumnSchema https://github.com/GreptimeTeam/greptimedb/blob/8959dbcef83507ccd76aaaffd2b44cab6426e68f/src/datatypes/src/schema.rs#L42

• Schema https://github.com/GreptimeTeam/greptimedb/blob/8959dbcef83507ccd76aaaffd2b44cab6426e68f/src/datatypes/src/schema.rs#L138

• RawSchema https://github.com/GreptimeTeam/greptimedb/blob/7ba512980a89b76f333af34fa55099f2ddab4d13/src/datatypes/src/schema/raw.rs#L24

• ProjectedSchema https://github.com/GreptimeTeam/greptimedb/blob/0791c65149efea7fa0acec67531878dbe37186a5/src/storage/src/schema/projected.rs#L105

• RegionSchema https://github.com/GreptimeTeam/greptimedb/blob/7ba512980a89b76f333af34fa55099f2ddab4d13/src/storage/src/schema/region.rs#L36

• StoreSchema https://github.com/GreptimeTeam/greptimedb/blob/7ba512980a89b76f333af34fa55099f2ddab4d13/src/storage/src/schema/store.rs#L35

Not to mention there are still arrow's Shema and Parquet's schema.

We need a doc to explain:

• why these schemas are required
• the relations and differences of these schemas
• when to use which schema
• how to convert these schemas to each other

Implementation challenges

NA

[waynexia]

Find another Schema in server:

https://github.com/GreptimeTeam/greptimedb/blob/e3785fca70c73860ea4cf69a4d3516296ca088ad/src/servers/src/http.rs#L103-L105

[evenyag]

https://github.com/GreptimeTeam/greptimedb/blob/7d29670c8636851f1a1d65fb385fbe5b04e297e0/src/storage/src/metadata.rs#L462

There is also a ColumnsMetadata in the RegionSchema https://github.com/GreptimeTeam/greptimedb/blob/7d29670c8636851f1a1d65fb385fbe5b04e297e0/src/storage/src/schema/region.rs#L44-L49

[MichaelScofield]

Now we have