Memberlist: Optimize conflictingTokensExist (#84)

This PR uses a memory pool instead of allocating a map for every time we call conflictingTokensExists to allow us to gc that memory easily and prevent long lived maps. Also switch to using a map[unit32]struct{} instead of a map[uint32]bool since we use the boolean as pretty much just a contains check.

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
+* [ENHANCEMENT] Optimise memberlist receive path when used as a backing store for rings with a large number of members. #76 #77 #84
 * [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
 * [BUGFIX] spanlogger: Support multiple tenant IDs. #59
 * [BUGFIX] Memberlist: fixed corrupted packets when sending compound messages with more than 255 messages or messages bigger than 64KB. #85

ring/model.go

@@ -4,6 +4,7 @@ import (
 	"container/heap"
 	"fmt"
 	"sort"
+	"sync"
 	"time"
 
 	"github.com/gogo/protobuf/proto"
@@ -302,19 +303,22 @@ func normalizeIngestersMap(inputRing *Desc) {
 	}
 }
 
-func conflictingTokensExist(normalizedIngesters map[string]InstanceDesc) bool {
-	count := 0
-	for _, ing := range normalizedIngesters {
-		count += len(ing.Tokens)
-	}
+var tokenMapPool = sync.Pool{New: func() interface{} { return make(map[uint32]struct{}) }}
 
-	tokensMap := make(map[uint32]bool, count)
+func conflictingTokensExist(normalizedIngesters map[string]InstanceDesc) bool {
+	tokensMap := tokenMapPool.Get().(map[uint32]struct{})
+	defer func() {
+		for k := range tokensMap {
+			delete(tokensMap, k)
+		}
+		tokenMapPool.Put(tokensMap)
+	}()
 	for _, ing := range normalizedIngesters {
 		for _, t := range ing.Tokens {
-			if tokensMap[t] {
+			if _, contains := tokensMap[t]; contains {
 				return true
 			}
-			tokensMap[t] = true
+			tokensMap[t] = struct{}{}
 		}
 	}
 	return false