[GitHub] [arrow-datafusion] tustvold commented on a diff in pull request #4606: Lazy system tables

[GitBox <gi...@apache.org>]

tustvold commented on code in PR #4606:
URL: https://github.com/apache/arrow-datafusion/pull/4606#discussion_r1047605470


##########
datafusion/core/src/catalog/information_schema.rs:
##########
@@ -220,74 +217,113 @@ impl InformationSchemaProvider {
                 }
             }
         }
-
-        let mem_table: MemTable = builder.into();
-
-        Arc::new(mem_table)
     }
 
     /// Construct the `information_schema.df_settings` virtual table
-    fn make_df_settings(&self) -> Arc<dyn TableProvider> {
-        let mut builder = InformationSchemaDfSettingsBuilder::new();
-
+    fn make_df_settings(&self, builder: &mut InformationSchemaDfSettingsBuilder) {
         for (name, setting) in self.config_options.read().options() {
             builder.add_setting(name, setting.to_string());
         }
-
-        let mem_table: MemTable = builder.into();
-
-        Arc::new(mem_table)
     }
 }
 
 impl SchemaProvider for InformationSchemaProvider {
-    fn as_any(&self) -> &(dyn any::Any + 'static) {
+    fn as_any(&self) -> &(dyn Any + 'static) {
         self
     }
 
     fn table_names(&self) -> Vec<String> {
-        vec![TABLES.to_string(), VIEWS.to_string(), COLUMNS.to_string()]
+        vec![
+            TABLES.to_string(),
+            VIEWS.to_string(),
+            COLUMNS.to_string(),
+            DF_SETTINGS.to_string(),
+        ]
     }
 
     fn table(&self, name: &str) -> Option<Arc<dyn TableProvider>> {
-        if name.eq_ignore_ascii_case("tables") {
-            Some(self.make_tables())
+        let config = self.config.clone();
+        let table: Arc<dyn PartitionStream> = if name.eq_ignore_ascii_case("tables") {
+            Arc::new(InformationSchemaTables::new(config))
         } else if name.eq_ignore_ascii_case("columns") {
-            Some(self.make_columns())
+            Arc::new(InformationSchemaColumns::new(config))
         } else if name.eq_ignore_ascii_case("views") {
-            Some(self.make_views())
+            Arc::new(InformationSchemaViews::new(config))
         } else if name.eq_ignore_ascii_case("df_settings") {
-            Some(self.make_df_settings())
+            Arc::new(InformationSchemaDfSettings::new(config))
         } else {
-            None
-        }
+            return None;
+        };
+
+        Some(Arc::new(
+            StreamingTable::try_new(table.schema().clone(), vec![table]).unwrap(),
+        ))
     }
 
     fn table_exist(&self, name: &str) -> bool {
         matches!(name.to_ascii_lowercase().as_str(), TABLES | VIEWS | COLUMNS)
     }
 }
 
+struct InformationSchemaTables {
+    schema: SchemaRef,
+    config: InformationSchemaConfig,
+}
+
+impl InformationSchemaTables {
+    fn new(config: InformationSchemaConfig) -> Self {
+        let schema = Arc::new(Schema::new(vec![
+            Field::new("table_catalog", DataType::Utf8, false),
+            Field::new("table_schema", DataType::Utf8, false),
+            Field::new("table_name", DataType::Utf8, false),
+            Field::new("table_type", DataType::Utf8, false),
+        ]));
+
+        Self { schema, config }
+    }
+
+    fn builder(&self) -> InformationSchemaTablesBuilder {
+        InformationSchemaTablesBuilder {
+            catalog_names: StringBuilder::new(),
+            schema_names: StringBuilder::new(),
+            table_names: StringBuilder::new(),
+            table_types: StringBuilder::new(),
+            schema: self.schema.clone(),
+        }
+    }
+}
+
+impl PartitionStream for InformationSchemaTables {

Review Comment:
   This is significantly less verbose than having to define a `TableProvider` and then a corresponding `ExecutionPlan`



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