planner: set the minimum Instance Plan Cache Mem Size to 100MiB (#57382)

ref #54057

Author: qw4990

pkg/planner/core/casetest/instanceplancache/BUILD.bazel

@@ -12,7 +12,7 @@ go_test(
         "others_test.go",
     ],
     flaky = True,
-    shard_count = 34,
+    shard_count = 35,
     deps = [
         "//pkg/parser/auth",
         "//pkg/testkit",

pkg/planner/core/casetest/instanceplancache/others_test.go

@@ -26,6 +26,19 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestInstancePlanCacheMinSize(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExecToErr("set global tidb_instance_plan_cache_max_size=0")
+	tk.MustExecToErr("set global tidb_instance_plan_cache_max_size=1")
+	tk.MustExecToErr("set global tidb_instance_plan_cache_max_size=101KiB")
+	tk.MustExecToErr("set global tidb_instance_plan_cache_max_size=10001KiB")
+	tk.MustExecToErr("set global tidb_instance_plan_cache_max_size=99MiB")
+	tk.MustExec("set global tidb_instance_plan_cache_max_size=100MiB")
+	tk.MustExec("set global tidb_instance_plan_cache_max_size=101MiB")
+	tk.MustExec("set global tidb_instance_plan_cache_max_size=2000000KiB")
+}
+
 func TestInstancePlanCacheVars(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 	tk := testkit.NewTestKit(t, store)
@@ -45,8 +58,8 @@ func TestInstancePlanCacheVars(t *testing.T) {
 	tk.MustExecToErr(`set global tidb_instance_plan_cache_max_size=-1`)
 	tk.MustExecToErr(`set global tidb_instance_plan_cache_max_size=-1111111111111`)
 	tk.MustExecToErr(`set global tidb_instance_plan_cache_max_size=dslfj`)
-	tk.MustExec(`set global tidb_instance_plan_cache_max_size=123456`)
-	tk.MustQuery(`select @@tidb_instance_plan_cache_max_size`).Check(testkit.Rows("123456"))
+	tk.MustExec(`set global tidb_instance_plan_cache_max_size=1234560000`)
+	tk.MustQuery(`select @@tidb_instance_plan_cache_max_size`).Check(testkit.Rows("1234560000"))
 	tk.MustExec(`set global tidb_instance_plan_cache_reserved_percentage=-1`)
 	tk.MustQuery(`show warnings`).Check(testkit.Rows(`Warning 1292 Truncated incorrect tidb_instance_plan_cache_reserved_percentage value: '-1'`))
 	tk.MustExec(`set global tidb_instance_plan_cache_reserved_percentage=1.1100`)

pkg/sessionctx/variable/sysvar.go

@@ -1419,6 +1419,9 @@ var defaultSysVars = []*SysVar{
 			if str == "" || v < 0 {
 				return errors.Errorf("invalid tidb_instance_plan_cache_max_mem_size value %s", val)
 			}
+			if v < MinTiDBInstancePlanCacheMemSize {
+				return errors.Errorf("tidb_instance_plan_cache_max_mem_size should be at least 100MiB")
+			}
 			InstancePlanCacheMaxMemSize.Store(int64(v))
 			return nil
 		}},

pkg/sessionctx/variable/tidb_vars.go

@@ -1469,6 +1469,7 @@ const (
 	DefTiDBNonPreparedPlanCacheSize                   = 100
 	DefTiDBPlanCacheMaxPlanSize                       = 2 * size.MB
 	DefTiDBInstancePlanCacheMaxMemSize                = 100 * size.MB
+	MinTiDBInstancePlanCacheMemSize                   = 100 * size.MB
 	DefTiDBInstancePlanCacheReservedPercentage        = 0.1
 	// MaxDDLReorgBatchSize is exported for testing.
 	MaxDDLReorgBatchSize                  int32  = 10240