Memberlist: Avoid checking for conflicting tokens if no tokens changed.

CHANGELOG.md

@@ -18,7 +18,7 @@
 * [ENHANCEMENT] Replace go-kit/kit/log with go-kit/log. #52
 * [ENHANCEMENT] Add spanlogger package. #42
 * [ENHANCEMENT] Add runutil.CloseWithLogOnErr function. #58
-* [ENHANCEMENT] Optimise memberlist receive path when used as a backing store for rings with a large number of members. #76 #77 #84
+* [ENHANCEMENT] Optimise memberlist receive path when used as a backing store for rings with a large number of members. #76 #77 #84 #91
 * [ENHANCEMENT] Memberlist: prepare the data to send on the write before starting counting the elapsed time for `-memberlist.packet-write-timeout`, in order to reduce chances we hit the timeout when sending a packet to other node. #89
 * [ENHANCEMENT] flagext: for cases such as `DeprecatedFlag()` that need a logger, add RegisterFlagsWithLogger. #80
 * [BUGFIX] spanlogger: Support multiple tenant IDs. #59

ring/model.go

@@ -202,11 +202,15 @@ func (d *Desc) mergeWithTime(mergeable memberlist.Mergeable, localCAS bool, now
 	otherIngesterMap := other.Ingesters
 
 	var updated []string
+	tokensChanged := false
 
 	for name, oing := range otherIngesterMap {
 		ting := thisIngesterMap[name]
 		// ting.Timestamp will be 0, if there was no such ingester in our version
 		if oing.Timestamp > ting.Timestamp {
+			if !tokensEqual(ting.Tokens, oing.Tokens) {
+				tokensChanged = true
+			}
 			oing.Tokens = append([]uint32(nil), oing.Tokens...) // make a copy of tokens
 			thisIngesterMap[name] = oing
 			updated = append(updated, name)
@@ -241,7 +245,7 @@ func (d *Desc) mergeWithTime(mergeable memberlist.Mergeable, localCAS bool, now
 	}
 
 	// resolveConflicts allocates lot of memory, so if we can avoid it, do that.
-	if conflictingTokensExist(thisIngesterMap) {
+	if tokensChanged && conflictingTokensExist(thisIngesterMap) {
 		resolveConflicts(thisIngesterMap)
 	}
 
@@ -303,6 +307,19 @@ func normalizeIngestersMap(inputRing *Desc) {
 	}
 }
 
+// tokensEqual checks for equality of two slices. Assumes the slices are sorted.
+func tokensEqual(lhs, rhs []uint32) bool {
+	if len(lhs) != len(rhs) {
+		return false
+	}
+	for i := 0; i < len(lhs); i++ {
+		if lhs[i] != rhs[i] {
+			return false
+		}
+	}
+	return true
+}
+
 var tokenMapPool = sync.Pool{New: func() interface{} { return make(map[uint32]struct{}) }}
 
 func conflictingTokensExist(normalizedIngesters map[string]InstanceDesc) bool {