executor: use sys session to build view for info_schema.columns retrieval (#33946) (#34251)

close #32459

Author: ti-srebot

executor/infoschema_reader_test.go

@@ -981,3 +981,63 @@ func (s *testInfoschemaTableSuite) TestTablesPKType(c *C) {
 	tk.MustQuery("SELECT TIDB_PK_TYPE FROM information_schema.tables where table_schema = 'test' and table_name = 't_common'").Check(testkit.Rows("CLUSTERED"))
 	tk.MustQuery("SELECT TIDB_PK_TYPE FROM information_schema.tables where table_schema = 'INFORMATION_SCHEMA' and table_name = 'TABLES'").Check(testkit.Rows("NONCLUSTERED"))
 }
+
+// https://github.com/pingcap/tidb/issues/32459.
+func (s *testInfoschemaTableSuite) TestJoinSystemTableContainsView(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t;")
+	tk.MustExec("drop view if exists v;")
+	tk.MustExec("create table t (a timestamp, b int);")
+	tk.MustExec("insert into t values (null, 100);")
+	tk.MustExec("create view v as select * from t;")
+	// This is used by grafana when TiDB is specified as the data source.
+	// See https://github.com/grafana/grafana/blob/e86b6662a187c77656f72bef3b0022bf5ced8b98/public/app/plugins/datasource/mysql/meta_query.ts#L31
+	for i := 0; i < 10; i++ {
+		tk.MustQuery(`
+SELECT
+    table_name as table_name,
+    ( SELECT
+        column_name as column_name
+      FROM information_schema.columns c
+      WHERE
+        c.table_schema = t.table_schema AND
+        c.table_name = t.table_name AND
+        c.data_type IN ('timestamp', 'datetime')
+      ORDER BY ordinal_position LIMIT 1
+    ) AS time_column,
+    ( SELECT
+        column_name AS column_name
+      FROM information_schema.columns c
+      WHERE
+        c.table_schema = t.table_schema AND
+        c.table_name = t.table_name AND
+        c.data_type IN('float', 'int', 'bigint')
+      ORDER BY ordinal_position LIMIT 1
+    ) AS value_column
+  FROM information_schema.tables t
+  WHERE
+    t.table_schema = database() AND
+    EXISTS
+    ( SELECT 1
+      FROM information_schema.columns c
+      WHERE
+        c.table_schema = t.table_schema AND
+        c.table_name = t.table_name AND
+        c.data_type IN ('timestamp', 'datetime')
+    ) AND
+    EXISTS
+    ( SELECT 1
+      FROM information_schema.columns c
+      WHERE
+        c.table_schema = t.table_schema AND
+        c.table_name = t.table_name AND
+        c.data_type IN('float', 'int', 'bigint')
+    )
+  LIMIT 1
+;
+`).Check(testkit.Rows("t a b"))
+	}
+	tk.MustExec("drop table if exists t;")
+	tk.MustExec("drop view if exists v;")
+}

executor/show.go

@@ -1761,7 +1761,13 @@ func (e *ShowExec) fetchShowBuiltins() error {
 // Because view's underlying table's column could change or recreate, so view's column type may change over time.
 // To avoid this situation we need to generate a logical plan and extract current column types from Schema.
 func tryFillViewColumnType(ctx context.Context, sctx sessionctx.Context, is infoschema.InfoSchema, dbName model.CIStr, tbl *model.TableInfo) error {
-	if tbl.IsView() {
+	if !tbl.IsView() {
+		return nil
+	}
+	// We need to run the build plan process in another session because there may be
+	// multiple goroutines running at the same time while session is not goroutine-safe.
+	// Take joining system table as an example, `fetchBuildSideRows` and `fetchProbeSideChunks` can be run concurrently.
+	return runWithSystemSession(sctx, func(s sessionctx.Context) error {
 		// Retrieve view columns info.
 		planBuilder, _ := plannercore.NewPlanBuilder(
 			plannercore.PlanBuilderOptNoExecution{}).Init(sctx, is, &hint.BlockHintProcessor{})
@@ -1780,6 +1786,23 @@ func tryFillViewColumnType(ctx context.Context, sctx sessionctx.Context, is info
 		} else {
 			return err
 		}
+		return nil
+	})
+}
+
+func runWithSystemSession(sctx sessionctx.Context, fn func(sessionctx.Context) error) error {
+	b := &baseExecutor{ctx: sctx}
+	sysCtx, err := b.getSysSession()
+	if err != nil {
+		return err
 	}
-	return nil
+	// TODO(tangenta): remove the CurrentDB assignment after
+	// https://github.com/pingcap/tidb/issues/34090 is fixed.
+	originDB := sysCtx.GetSessionVars().CurrentDB
+	sysCtx.GetSessionVars().CurrentDB = sctx.GetSessionVars().CurrentDB
+	defer func() {
+		sysCtx.GetSessionVars().CurrentDB = originDB
+	}()
+	defer b.releaseSysSession(sysCtx)
+	return fn(sysCtx)
 }