Remove engine on close

CHANGELOG.md

@@ -38,6 +38,7 @@
 - [#5479](https://github.com/influxdata/influxdb/issues/5479): Bringing up a node as a meta only node causes panic
 - [#5504](https://github.com/influxdata/influxdb/issues/5475): create retention policy on unexistant DB crash InfluxDB
 - [#5505](https://github.com/influxdata/influxdb/issues/5505): Clear authCache in meta.Client when password changes.
+- [#5244](https://github.com/influxdata/influxdb/issues/5244): panic: ensure it's safe to close engine multiple times.
 
 ## v0.9.6 [2015-12-09]
 

tsdb/shard.go

@@ -146,10 +146,15 @@ func (s *Shard) Close() error {
 }
 
 func (s *Shard) close() error {
-	if s.engine != nil {
-		return s.engine.Close()
+	if s.engine == nil {
+		return nil
 	}
-	return nil
+
+	err := s.engine.Close()
+	if err == nil {
+		s.engine = nil
+	}
+	return err
 }
 
 // DiskSize returns the size on disk of this shard