feat(cubestore): Support EXPLAIN for meta queries

rust/cubestore/cubestore/src/queryplanner/pretty_printers.rs

@@ -30,7 +30,7 @@ use crate::queryplanner::serialized_plan::{IndexSnapshot, RowRange};
 use crate::queryplanner::tail_limit::TailLimitExec;
 use crate::queryplanner::topk::ClusterAggregateTopK;
 use crate::queryplanner::topk::{AggregateTopKExec, SortColumn};
-use crate::queryplanner::CubeTableLogical;
+use crate::queryplanner::{CubeTableLogical, InfoSchemaTableProvider};
 use datafusion::cube_ext::join::CrossJoinExec;
 use datafusion::cube_ext::joinagg::CrossJoinAggExec;
 use datafusion::cube_ext::rolling::RollingWindowAggExec;
@@ -257,6 +257,12 @@ fn pp_source(t: &dyn TableProvider) -> String {
         format!("CubeTable(index: {})", pp_index(t.index_snapshot()))
     } else if let Some(t) = t.as_any().downcast_ref::<InlineTableProvider>() {
         format!("InlineTableProvider(data: {} rows)", t.get_data().len())
+    } else if t
+        .as_any()
+        .downcast_ref::<InfoSchemaTableProvider>()
+        .is_some()
+    {
+        "InfoSchemaTableProvider".to_string()
     } else {
         panic!("unknown table provider");
     }

rust/cubestore/cubestore/src/sql/mod.rs

@@ -461,9 +461,23 @@ impl SqlServiceImpl {
                 };
                 Ok(res)
             }
-            _ => Err(CubeError::user(
-                "Explain not supported for selects from system tables".to_string(),
-            )),
+            QueryPlan::Meta(logical_plan) => {
+                if !analyze {
+                    Ok(DataFrame::new(
+                        vec![Column::new(
+                            "logical plan".to_string(),
+                            ColumnType::String,
+                            0,
+                        )],
+                        vec![Row::new(vec![TableValue::String(pp_plan(&logical_plan))])],
+                    ))
+                } else {
+                    Err(CubeError::user(
+                        "EXPLAIN ANALYZE is not supported for selects from system tables"
+                            .to_string(),
+                    ))
+                }
+            }
         }?;
         Ok(Arc::new(res))
     }
@@ -3834,6 +3848,33 @@ mod tests {
             )
     }
 
+    #[tokio::test]
+    async fn explain_meta_logical_plan() {
+        Config::run_test("explain_meta_logical_plan", async move |services| {
+            let service = services.sql_service;
+            service.exec_query("CREATE SCHEMA foo").await.unwrap();
+
+            let result = service.exec_query(
+                "EXPLAIN SELECT table_name FROM information_schema.tables WHERE table_schema = 'foo'"
+            ).await.unwrap();
+            assert_eq!(result.len(), 1);
+            assert_eq!(result.get_columns().len(), 1);
+
+            let pp_plan = match &result
+                .get_rows()[0]
+                .values()[0] {
+                TableValue::String(pp_plan) => pp_plan,
+                _ => {assert!(false); ""}
+            };
+            assert_eq!(
+                pp_plan,
+                "Projection, [information_schema.tables.table_name]\
+                \n  Filter\
+                \n    Scan information_schema.tables, source: InfoSchemaTableProvider, fields: [table_schema, table_name]"
+            );
+        }).await;
+    }
+
     #[tokio::test]
     async fn explain_logical_plan() {
         Config::run_test("explain_logical_plan", async move |services| {
@@ -3868,6 +3909,7 @@ mod tests {
             );
         }).await;
     }
+
     #[tokio::test]
     async fn explain_physical_plan() {
         Config::test("explain_analyze_router").update_config(|mut config| {
@@ -3878,7 +3920,7 @@ mod tests {
         }).start_test(async move |services| {
             let service = services.sql_service;
 
-            Config::test("expalain_analyze_worker_1").update_config(|mut config| {
+            Config::test("explain_analyze_worker_1").update_config(|mut config| {
                 config.worker_bind_address = Some("127.0.0.1:14006".to_string());
                 config.server_name = "127.0.0.1:14006".to_string();
                 config.metastore_remote_address = Some("127.0.0.1:15006".to_string());