doamin: fix GetSnapshotInfoSchema using current TS (#10309)

Author: zimulala

domain/domain.go

@@ -218,14 +218,10 @@ func isTooOldSchema(usedVersion, newVersion int64) bool {
 // The second returned value is the delta updated table IDs.
 func (do *Domain) tryLoadSchemaDiffs(m *meta.Meta, usedVersion, newVersion int64) (bool, []int64, error) {
 	// If there isn't any used version, or used version is too old, we do full load.
+	// And when users use history read feature, we will set usedVersion to initialVersion, then full load is needed.
 	if isTooOldSchema(usedVersion, newVersion) {
 		return false, nil, nil
 	}
-	if usedVersion > newVersion {
-		// When user use History Read feature, history schema will be loaded.
-		// usedVersion may be larger than newVersion, full load is needed.
-		return false, nil, nil
-	}
 	var diffs []*model.SchemaDiff
 	for usedVersion < newVersion {
 		usedVersion++
@@ -260,7 +256,8 @@ func (do *Domain) InfoSchema() infoschema.InfoSchema {
 // GetSnapshotInfoSchema gets a snapshot information schema.
 func (do *Domain) GetSnapshotInfoSchema(snapshotTS uint64) (infoschema.InfoSchema, error) {
 	snapHandle := do.infoHandle.EmptyClone()
-	_, _, _, err := do.loadInfoSchema(snapHandle, do.infoHandle.Get().SchemaMetaVersion(), snapshotTS)
+	// For the snapHandle, it's an empty Handle, so its usedSchemaVersion is initialVersion.
+	_, _, _, err := do.loadInfoSchema(snapHandle, initialVersion, snapshotTS)
 	if err != nil {
 		return nil, err
 	}

domain/domain_test.go

@@ -26,6 +26,7 @@ import (
 	"github.com/pingcap/parser/mysql"
 	"github.com/pingcap/tidb/metrics"
 	"github.com/pingcap/tidb/store/mockstore"
+	"github.com/pingcap/tidb/store/tikv/oracle"
 	"github.com/pingcap/tidb/util/mock"
 	"github.com/pingcap/tidb/util/testleak"
 	dto "github.com/prometheus/client_model/go"
@@ -63,6 +64,7 @@ func (*testSuite) TestT(c *C) {
 	store = dom.Store()
 	ctx := mock.NewContext()
 	ctx.Store = store
+	snapTS := oracle.EncodeTSO(oracle.GetPhysical(time.Now()))
 	dd := dom.DDL()
 	c.Assert(dd, NotNil)
 	c.Assert(dd.GetLease(), Equals, 80*time.Millisecond)
@@ -78,6 +80,16 @@ func (*testSuite) TestT(c *C) {
 	// for setting lease
 	lease := 100 * time.Millisecond
 
+	// for GetSnapshotInfoSchema
+	snapIs, err := dom.GetSnapshotInfoSchema(snapTS)
+	c.Assert(err, IsNil)
+	c.Assert(snapIs, NotNil)
+	snapTS = oracle.EncodeTSO(oracle.GetPhysical(time.Now()))
+	snapIs, err = dom.GetSnapshotInfoSchema(snapTS)
+	c.Assert(err, IsNil)
+	c.Assert(snapIs, NotNil)
+	c.Assert(snapIs.SchemaMetaVersion(), Equals, is.SchemaMetaVersion())
+
 	// for schemaValidator
 	schemaVer := dom.SchemaValidator.(*schemaValidator).latestSchemaVer
 	ver, err := store.CurrentVersion()