perf: pre-allocate all known length arrays to avoid re-scaling (#5029)

Co-authored-by: Kevin Wan <wanjunfeng@gmail.com>

core/conf/config.go

@@ -316,7 +316,7 @@ func toLowerCaseInterface(v any, info *fieldInfo) any {
 	case map[string]any:
 		return toLowerCaseKeyMap(vv, info)
 	case []any:
-		var arr []any
+		arr := make([]any, 0, len(vv))
 		for _, vvv := range vv {
 			arr = append(arr, toLowerCaseInterface(vvv, info))
 		}

core/discov/internal/registry.go

@@ -207,7 +207,7 @@ func (c *cluster) getCurrent(key watchKey) []KV {
 		return nil
 	}
 
-	var kvs []KV
+	kvs := make([]KV, 0, len(watcher.values))
 	for k, v := range watcher.values {
 		kvs = append(kvs, KV{
 			Key: k,
@@ -308,7 +308,7 @@ func (c *cluster) load(cli EtcdClient, key watchKey) int64 {
 		time.Sleep(coolDownUnstable.AroundDuration(coolDownInterval))
 	}
 
-	var kvs []KV
+	kvs := make([]KV, 0, len(resp.Kvs))
 	for _, ev := range resp.Kvs {
 		kvs = append(kvs, KV{
 			Key: string(ev.Key),
@@ -352,7 +352,7 @@ func (c *cluster) reload(cli EtcdClient) {
 	// cancel the previous watches
 	close(c.done)
 	c.watchGroup.Wait()
-	var keys []watchKey
+	keys := make([]watchKey, 0, len(c.watchers))
 	for wk, wval := range c.watchers {
 		keys = append(keys, wk)
 		if wval.cancel != nil {

core/logx/rotatelogger.go

@@ -211,7 +211,7 @@ func (r *SizeLimitRotateRule) OutdatedFiles() []string {
 		}
 	}
 
-	var result []string
+	result := make([]string, 0, len(outdated))
 	for k := range outdated {
 		result = append(result, k)
 	}

core/stores/redis/redis.go

@@ -1944,7 +1944,7 @@ func (s *Redis) ZaddsCtx(ctx context.Context, key string, ps ...Pair) (int64, er
 		return 0, err
 	}
 
-	var zs []red.Z
+	zs := make([]red.Z, 0, len(ps))
 	for _, p := range ps {
 		z := red.Z{Score: float64(p.Score), Member: p.Key}
 		zs = append(zs, z)