feat: add SchemaProvider::table_type(table_name: &str)

InformationSchemaConfig::make_tables only needs the TableType not the
whole TableProvider, and the former may require an expensive catalog
operation to construct and the latter may not.

This allows avoiding `SELECT * FROM information_schema.tables` having to
make 1 of those potentially expensive operations per table.

Author: epgif

datafusion/catalog/src/schema.rs

@@ -54,6 +54,15 @@ pub trait SchemaProvider: Debug + Sync + Send {
         name: &str,
     ) -> Result<Option<Arc<dyn TableProvider>>, DataFusionError>;
 
+    /// Retrieves the type of a specific table from the schema by name, if it exists,
+    /// otherwise returns `None`.
+    async fn table_type(
+        &self,
+        name: &str,
+    ) -> Result<Option<datafusion_expr::TableType>, DataFusionError> {
+        self.table(name).await.map(|o| o.map(|t| t.table_type()))
+    }
+
     /// If supported by the implementation, adds a new table named `name` to
     /// this schema.
     ///

datafusion/core/src/catalog_common/information_schema.rs

@@ -104,12 +104,15 @@ impl InformationSchemaConfig {
                     // schema name may not exist in the catalog, so we need to check
                     if let Some(schema) = catalog.schema(&schema_name) {
                         for table_name in schema.table_names() {
-                            if let Some(table) = schema.table(&table_name).await? {
+                            // TODO(epg): Why is it legal for SchemaProvider::table to return None
+                            // for a name returned by SchemaProvider::table_names?  Shouldn't we
+                            // assert Some rather than quietly continuing?
+                            if let Some(table_type) = schema.table_type(&table_name).await? {
                                 builder.add_table(
                                     &catalog_name,
                                     &schema_name,
                                     &table_name,
-                                    table.table_type(),
+                                    table_type,
                                 );
                             }
                         }