filer prefer volume server in same data center (#3405)

* initial prefer same data center
https://github.com/seaweedfs/seaweedfs/issues/3404

* GetDataCenter

* prefer same data center for ReplicationSource

* GetDataCenterId

* remove glog

1 files changed, 15 insertions, 7 deletions

diff --git a/weed/filer/reader_at.go b/weed/filer/reader_at.go
index 70228705b..2b3e77d1b 100644
--- a/weed/filer/reader_at.go
+++ b/weed/filer/reader_at.go
@@ -66,17 +66,25 @@ func LookupFn(filerClient filer_pb.FilerClient) wdclient.LookupFileIdFunctionTyp
 			return nil, err
 		}
 
+		fcDataCenter := filerClient.GetDataCenter()
+		var sameDcTargetUrls, otherTargetUrls []string
 		for _, loc := range locations.Locations {
 			volumeServerAddress := filerClient.AdjustedUrl(loc)
 			targetUrl := fmt.Sprintf("http://%s/%s", volumeServerAddress, fileId)
-			targetUrls = append(targetUrls, targetUrl)
-		}
-
-		for i := len(targetUrls) - 1; i > 0; i-- {
-			j := rand.Intn(i + 1)
-			targetUrls[i], targetUrls[j] = targetUrls[j], targetUrls[i]
+			if fcDataCenter == "" || fcDataCenter != loc.DataCenter {
+				otherTargetUrls = append(otherTargetUrls, targetUrl)
+			} else {
+				sameDcTargetUrls = append(sameDcTargetUrls, targetUrl)
+			}
 		}
-
+		rand.Shuffle(len(sameDcTargetUrls), func(i, j int) {
+			sameDcTargetUrls[i], sameDcTargetUrls[j] = sameDcTargetUrls[j], sameDcTargetUrls[i]
+		})
+		rand.Shuffle(len(otherTargetUrls), func(i, j int) {
+			otherTargetUrls[i], otherTargetUrls[j] = otherTargetUrls[j], otherTargetUrls[i]
+		})
+		// Prefer same data center
+		targetUrls = append(sameDcTargetUrls, otherTargetUrls...)
 		return
 	}
 }