planner, config: Enable plan cache by default

bindinfo/bind_test.go

@@ -31,6 +31,7 @@ import (
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/meta/autoid"
 	"github.com/pingcap/tidb/metrics"
+	plannercore "github.com/pingcap/tidb/planner/core"
 	"github.com/pingcap/tidb/session"
 	"github.com/pingcap/tidb/store/mockstore"
 	"github.com/pingcap/tidb/store/mockstore/cluster"
@@ -604,6 +605,13 @@ func (s *testSuite) TestErrorBind(c *C) {
 func (s *testSuite) TestPreparedStmt(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	s.cleanBindingEnv(tk)
+
+	orgEnable := plannercore.PreparedPlanCacheEnabled()
+	defer func() {
+		plannercore.SetPreparedPlanCache(orgEnable)
+	}()
+	plannercore.SetPreparedPlanCache(false) // requires plan cache disabled, or the IndexNames = 1 on first test.
+
 	tk.MustExec("use test")
 	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t(a int, b int, index idx(a))")

config/config.go

@@ -677,7 +677,7 @@ var defaultConf = Config{
 		HeaderTimeout: 5,
 	},
 	PreparedPlanCache: PreparedPlanCache{
-		Enabled:          false,
+		Enabled:          true,
 		Capacity:         100,
 		MemoryGuardRatio: 0.1,
 	},

config/config.toml.example

@@ -286,7 +286,7 @@ networks = ""
 header-timeout = 5
 
 [prepared-plan-cache]
-enabled = false
+enabled = true
 capacity = 100
 memory-guard-ratio = 0.1
 

executor/prepared_test.go

@@ -69,6 +69,12 @@ func (s *testSerialSuite) TestPrepareStmtAfterIsolationReadChange(c *C) {
 	tk := testkit.NewTestKitWithInit(c, s.store)
 	tk.Se.Auth(&auth.UserIdentity{Username: "root", Hostname: "localhost", CurrentUser: true, AuthUsername: "root", AuthHostname: "%"}, nil, []byte("012345678901234567890"))
 
+	orgEnable := plannercore.PreparedPlanCacheEnabled()
+	defer func() {
+		plannercore.SetPreparedPlanCache(orgEnable)
+	}()
+	plannercore.SetPreparedPlanCache(false) // requires plan cache disabled
+
 	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t(a int)")
 	// create virtual tiflash replica.

expression/integration_test.go

@@ -5593,6 +5593,24 @@ func (s *testIntegrationSuite) TestCastStrToInt(c *C) {
 	}
 }
 
+func (s *testIntegrationSerialSuite) TestPreparePlanCache(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+
+	// Plan cache should now be on by default
+	c.Assert(plannercore.PreparedPlanCacheEnabled(), Equals, true)
+
+	// Use the example from the docs https://docs.pingcap.com/tidb/stable/sql-prepare-plan-cache
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t;")
+	tk.MustExec("create table t(a int);")
+	tk.MustExec("prepare stmt from 'select * from t where a = ?';")
+	tk.MustExec("set @a = 1;")
+	tk.MustExec("execute stmt using @a;")
+	tk.MustQuery("select @@last_plan_from_cache;").Check(testkit.Rows("0"))
+	tk.MustExec("execute stmt using @a;")
+	tk.MustQuery("select @@last_plan_from_cache;").Check(testkit.Rows("1"))
+}
+
 func (s *testIntegrationSerialSuite) TestIssue16205(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	orgEnable := plannercore.PreparedPlanCacheEnabled()

planner/core/cache.go

@@ -32,9 +32,8 @@ import (
 
 var (
 	// preparedPlanCacheEnabledValue stores the global config "prepared-plan-cache-enabled".
-	// If the value of "prepared-plan-cache-enabled" is true, preparedPlanCacheEnabledValue's value is 1.
-	// Otherwise, preparedPlanCacheEnabledValue's value is 0.
-	preparedPlanCacheEnabledValue int32
+	// The value is true unless "prepared-plan-cache-enabled" is FALSE in configuration.
+	preparedPlanCacheEnabledValue int32 = 1
 	// PreparedPlanCacheCapacity stores the global config "prepared-plan-cache-capacity".
 	PreparedPlanCacheCapacity uint = 100
 	// PreparedPlanCacheMemoryGuardRatio stores the global config "prepared-plan-cache-memory-guard-ratio".