test(dm): fix upstream switch CI and reduce versions in upgrading CI (#…

…6502)

ref #4159

.github/workflows/upgrade_dm_via_tiup.yaml

@@ -77,7 +77,7 @@ jobs:
       fail-fast: false
       matrix:
         previous_v2:
-          ["v2.0.0", "v2.0.1", "v2.0.3", "v2.0.4", "v2.0.5", "v2.0.6", "v2.0.7", "v5.3.0"]
+          ["v2.0.1", "v2.0.7", "v5.3.0"]
 
     steps:
       - name: Set up Go 1.18

dm/syncer/checkpoint.go

@@ -422,7 +422,16 @@ func (cp *RemoteCheckPoint) Snapshot(isSyncFlush bool) *SnapshotInfo {
 		}
 	}
 
-	flushGlobalPoint := cp.globalPoint.outOfDate() || cp.globalPointSaveTime.IsZero() || (isSyncFlush && cp.needFlushSafeModeExitPoint.Load())
+	// flush when
+	// - global checkpoint is forwarded
+	// - global checkpoint is not forwarded but binlog filename updated. This may happen when upstream switched or relay
+	//   enable/disable in GTID replication
+	// - the first time to flush checkpoint
+	// - need update safe mode exit point
+	flushGlobalPoint := cp.globalPoint.outOfDate() ||
+		cp.globalPoint.savedPoint.location.Position.Name != cp.globalPoint.flushedPoint.location.Position.Name ||
+		cp.globalPointSaveTime.IsZero() ||
+		(isSyncFlush && cp.needFlushSafeModeExitPoint.Load())
 
 	// if there is no change on both table points and global point, just return an empty snapshot
 	if len(tableCheckPoints) == 0 && !flushGlobalPoint {