session: fix unseccessfully isolation read engines init session (#16465)

sessionctx/variable/sysvar.go

@@ -730,7 +730,6 @@ var defaultSysVars = []*SysVar{
 	{ScopeGlobal | ScopeSession, TiDBStmtSummaryHistorySize, strconv.Itoa(config.GetGlobalConfig().StmtSummary.HistorySize)},
 	{ScopeSession, TiDBIsolationReadEngines, strings.Join(config.GetGlobalConfig().IsolationRead.Engines, ", ")},
 	{ScopeGlobal | ScopeSession, TiDBStoreLimit, strconv.FormatInt(atomic.LoadInt64(&config.GetGlobalConfig().TiKVClient.StoreLimit), 10)},
-	{ScopeGlobal | ScopeSession, TiDBIsolationReadEngines, "tikv,tiflash"},
 }
 
 // SynonymsSysVariables is synonyms of system variables.

tidb-server/main.go

@@ -20,6 +20,7 @@ import (
 	"os"
 	"runtime"
 	"strconv"
+	"strings"
 	"sync/atomic"
 	"time"
 
@@ -517,6 +518,7 @@ func setGlobalVars() {
 	variable.SysVars[variable.Socket].Value = cfg.Socket
 	variable.SysVars[variable.DataDir].Value = cfg.Path
 	variable.SysVars[variable.TiDBSlowQueryFile].Value = cfg.Log.SlowQueryFile
+	variable.SysVars[variable.TiDBIsolationReadEngines].Value = strings.Join(cfg.IsolationRead.Engines, ", ")
 
 	// For CI environment we default enable prepare-plan-cache.
 	plannercore.SetPreparedPlanCache(config.CheckTableBeforeDrop || cfg.PreparedPlanCache.Enabled)

tidb-server/main_test.go

@@ -13,7 +13,13 @@
 
 package main
 
-import "testing"
+import (
+	"testing"
+
+	. "github.com/pingcap/check"
+	"github.com/pingcap/tidb/config"
+	"github.com/pingcap/tidb/sessionctx/variable"
+)
 
 var isCoverageServer = "0"
 
@@ -24,3 +30,24 @@ func TestRunMain(t *testing.T) {
 		main()
 	}
 }
+
+func TestT(t *testing.T) {
+	TestingT(t)
+}
+
+var _ = Suite(&testMainSuite{})
+
+type testMainSuite struct{}
+
+func (t *testMainSuite) TestSetGlobalVars(c *C) {
+	c.Assert(variable.SysVars[variable.TiDBIsolationReadEngines].Value, Equals, "tikv, tiflash")
+	c.Assert(variable.SysVars[variable.TIDBMemQuotaQuery].Value, Equals, "34359738368")
+
+	loadConfig()
+	config.GetGlobalConfig().IsolationRead.Engines = []string{"tikv"}
+	config.GetGlobalConfig().MemQuotaQuery = 9999999
+	setGlobalVars()
+
+	c.Assert(variable.SysVars[variable.TiDBIsolationReadEngines].Value, Equals, "tikv")
+	c.Assert(variable.SysVars[variable.TIDBMemQuotaQuery].Value, Equals, "9999999")
+}