Errant GTID detection fix for VTOrc (#17287)

Signed-off-by: Manan Gupta <manan@planetscale.com>

go/vt/vtorc/inst/instance_dao.go

@@ -362,7 +362,7 @@ Cleanup:
 		// Add replication group ancestry UUID as well. Otherwise, VTOrc thinks there are errant GTIDs in group
 		// members and its replicas, even though they are not.
 		instance.AncestryUUID = strings.Trim(instance.AncestryUUID, ",")
-		err = detectErrantGTIDs(tabletAlias, instance, tablet)
+		err = detectErrantGTIDs(instance, tablet)
 	}
 
 	latency.Stop("instance")
@@ -390,13 +390,18 @@ Cleanup:
 }
 
 // detectErrantGTIDs detects the errant GTIDs on an instance.
-func detectErrantGTIDs(tabletAlias string, instance *Instance, tablet *topodatapb.Tablet) (err error) {
+func detectErrantGTIDs(instance *Instance, tablet *topodatapb.Tablet) (err error) {
 	// If the tablet is not replicating from anyone, then it could be the previous primary.
 	// We should check for errant GTIDs by finding the difference with the shard's current primary.
 	if instance.primaryExecutedGtidSet == "" && instance.SourceHost == "" {
 		var primaryInstance *Instance
 		primaryAlias, _, _ := ReadShardPrimaryInformation(tablet.Keyspace, tablet.Shard)
 		if primaryAlias != "" {
+			// Check if the current tablet is the primary.
+			// If it is, then we don't need to run errant gtid detection on it.
+			if primaryAlias == instance.InstanceAlias {
+				return nil
+			}
 			primaryInstance, _, _ = ReadInstance(primaryAlias)
 		}
 		// Only run errant GTID detection, if we are sure that the data read of the current primary
@@ -434,7 +439,7 @@ func detectErrantGTIDs(tabletAlias string, instance *Instance, tablet *topodatap
 			if err == nil {
 				var gtidCount int64
 				gtidCount, err = replication.GTIDCount(instance.GtidErrant)
-				currentErrantGTIDCount.Set(tabletAlias, gtidCount)
+				currentErrantGTIDCount.Set(instance.InstanceAlias, gtidCount)
 			}
 		}
 	}

go/vt/vtorc/inst/instance_dao_test.go

@@ -854,7 +854,7 @@ func TestDetectErrantGTIDs(t *testing.T) {
 	primaryTablet := &topodatapb.Tablet{
 		Alias: &topodatapb.TabletAlias{
 			Cell: "zone-1",
-			Uid:  100,
+			Uid:  101,
 		},
 		Keyspace: keyspaceName,
 		Shard:    shardName,
@@ -881,7 +881,8 @@ func TestDetectErrantGTIDs(t *testing.T) {
 				require.NoError(t, err)
 			}
 
-			err = detectErrantGTIDs(topoproto.TabletAliasString(tablet.Alias), tt.instance, tablet)
+			tt.instance.InstanceAlias = topoproto.TabletAliasString(tablet.Alias)
+			err = detectErrantGTIDs(tt.instance, tablet)
 			if tt.wantErr {
 				require.Error(t, err)
 				return
@@ -891,3 +892,47 @@ func TestDetectErrantGTIDs(t *testing.T) {
 		})
 	}
 }
+
+// TestPrimaryErrantGTIDs tests that we don't run Errant GTID detection on the primary tablet itself!
+func TestPrimaryErrantGTIDs(t *testing.T) {
+	// Clear the database after the test. The easiest way to do that is to run all the initialization commands again.
+	defer func() {
+		db.ClearVTOrcDatabase()
+	}()
+	db.ClearVTOrcDatabase()
+	keyspaceName := "ks"
+	shardName := "0"
+	tablet := &topodatapb.Tablet{
+		Alias: &topodatapb.TabletAlias{
+			Cell: "zone-1",
+			Uid:  100,
+		},
+		Keyspace: keyspaceName,
+		Shard:    shardName,
+	}
+	instance := &Instance{
+		SourceHost:      "",
+		ExecutedGtidSet: "230ea8ea-81e3-11e4-972a-e25ec4bd140a:1-10589,8bc65c84-3fe4-11ed-a912-257f0fcdd6c9:1-34,316d193c-70e5-11e5-adb2-ecf4bb2262ff:1-341",
+		InstanceAlias:   topoproto.TabletAliasString(tablet.Alias),
+	}
+
+	// Save shard record for the primary tablet.
+	err := SaveShard(topo.NewShardInfo(keyspaceName, shardName, &topodatapb.Shard{
+		PrimaryAlias: tablet.Alias,
+	}, nil))
+	require.NoError(t, err)
+
+	// Store the tablet record and the instance.
+	err = SaveTablet(tablet)
+	require.NoError(t, err)
+	err = WriteInstance(instance, true, nil)
+	require.NoError(t, err)
+
+	// After this if we read a new information for the record that updates its
+	// gtid set further, we shouldn't be detecting errant GTIDs on it since it is the primary!
+	// We shouldn't be comparing it with a previous version of itself!
+	instance.ExecutedGtidSet = "230ea8ea-81e3-11e4-972a-e25ec4bd140a:1-10589,8bc65c84-3fe4-11ed-a912-257f0fcdd6c9:1-34,316d193c-70e5-11e5-adb2-ecf4bb2262ff:1-351"
+	err = detectErrantGTIDs(instance, tablet)
+	require.NoError(t, err)
+	require.EqualValues(t, "", instance.GtidErrant)
+}