From 8c6dbedb300afeca24b1e656cd950c7fd702bfb9 Mon Sep 17 00:00:00 2001
From: Weizhen Wang <wangweizhen@pingcap.com>
Date: Mon, 28 Jul 2025 20:20:27 +0800
Subject: [PATCH] filter: no need to always convert dbname to lowercase in
 IsSystemSchema (#62657)

close pingcap/tidb#62658
---
 pkg/planner/core/plan_cacheable_checker.go | 2 +-
 pkg/util/filter/BUILD.bazel                | 6 +++++-
 pkg/util/filter/schema.go                  | 5 ++++-
 pkg/util/filter/schema_test.go             | 4 +++-
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/pkg/planner/core/plan_cacheable_checker.go b/pkg/planner/core/plan_cacheable_checker.go
index 9f8de75978..fcf8188e92 100644
--- a/pkg/planner/core/plan_cacheable_checker.go
+++ b/pkg/planner/core/plan_cacheable_checker.go
@@ -495,7 +495,7 @@ func (checker *nonPreparedPlanCacheableChecker) Enter(in ast.Node) (out ast.Node
 		}
 		return in, !checker.cacheable
 	case *ast.TableName:
-		if filter.IsSystemSchema(node.Schema.O) {
+		if filter.IsSystemSchema(node.Schema.L) {
 			checker.cacheable = false
 			checker.reason = "access tables in system schema"
 			return in, !checker.cacheable
diff --git a/pkg/util/filter/BUILD.bazel b/pkg/util/filter/BUILD.bazel
index bb65332ea4..dca1528bf2 100644
--- a/pkg/util/filter/BUILD.bazel
+++ b/pkg/util/filter/BUILD.bazel
@@ -10,6 +10,7 @@ go_library(
     visibility = ["//visibility:public"],
     deps = [
         "//pkg/meta/metadef",
+        "//pkg/util/intest",
         "//pkg/util/table-filter",
         "//pkg/util/table-rule-selector",
         "@com_github_pingcap_errors//:errors",
@@ -25,5 +26,8 @@ go_test(
     ],
     embed = [":filter"],
     flaky = True,
-    deps = ["@com_github_stretchr_testify//require"],
+    deps = [
+        "//pkg/parser/ast",
+        "@com_github_stretchr_testify//require",
+    ],
 )
diff --git a/pkg/util/filter/schema.go b/pkg/util/filter/schema.go
index 04106b6d3c..0503af2972 100644
--- a/pkg/util/filter/schema.go
+++ b/pkg/util/filter/schema.go
@@ -18,6 +18,7 @@ import (
 	"strings"
 
 	"github.com/pingcap/tidb/pkg/meta/metadef"
+	"github.com/pingcap/tidb/pkg/util/intest"
 )
 
 var (
@@ -30,7 +31,9 @@ var (
 // IsSystemSchema checks whether schema is system schema or not.
 // case insensitive
 func IsSystemSchema(schema string) bool {
-	schema = strings.ToLower(schema)
+	intest.AssertFunc(func() bool {
+		return schema == strings.ToLower(schema)
+	})
 	return schema == DMHeartbeatSchema || schema == InspectionSchemaName ||
 		metadef.IsMemOrSysDB(schema)
 }
diff --git a/pkg/util/filter/schema_test.go b/pkg/util/filter/schema_test.go
index 2ee873f358..d9c44ccf51 100644
--- a/pkg/util/filter/schema_test.go
+++ b/pkg/util/filter/schema_test.go
@@ -17,6 +17,7 @@ package filter
 import (
 	"testing"
 
+	"github.com/pingcap/tidb/pkg/parser/ast"
 	"github.com/stretchr/testify/require"
 )
 
@@ -39,6 +40,7 @@ func TestIsSystemSchema(t *testing.T) {
 	}
 
 	for _, tt := range cases {
-		require.Equalf(t, tt.expected, IsSystemSchema(tt.name), "schema name = %s", tt.name)
+		name := ast.NewCIStr(tt.name)
+		require.Equalf(t, tt.expected, IsSystemSchema(name.L), "schema name = %s", tt.name)
 	}
 }