fast reorg checkpoint has wrong prerequisite

[lance6716]

If the checkpoint record shows the it is generated by current node

tidb/pkg/ddl/ingest/checkpoint.go

Lines 307 to 308 in c24dca5

	if s.instanceAddr == cp.InstanceAddr || cp.InstanceAddr == "" /* initial state */ {
	s.localDataIsValid = true

we skip the data whose key is smaller that "local storage key watermark" and assume the data is already stay in local storage.

tidb/pkg/ddl/ingest/checkpoint.go

Lines 128 to 137 in c24dca5

	// IsComplete checks if the task is complete.
	// This is called before the reader reads the data and decides whether to skip the current task.
	func (s *CheckpointManager) IsComplete(end kv.Key) bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	if len(s.minKeySyncGlobal) > 0 && end.Cmp(s.minKeySyncGlobal) <= 0 {
	return true
	}
	return s.localDataIsValid && len(s.minKeySyncLocal) > 0 && end.Cmp(s.minKeySyncLocal) <= 0
	}

However this is not reliable, especially we are using /tmp folder to store the data https://docs.pingcap.com/tidb/stable/command-line-flags-for-tidb-configuration#--temp-dir. If the node restarts in many OS /tmp folder will be cleaned.