Merge pull request #2441 from influxdata/preallocate_groupid

perf: preallocate GroupID

CHANGELOG.md

@@ -6,6 +6,7 @@
 - [#1839](https://github.com/influxdata/kapacitor/pull/1839): Add Subscription path configuration option to allow Kapacitor to run behind a reverse proxy, thanks @aspring
 - [#2055](https://github.com/influxdata/kapacitor/pull/2055): Add support for correlate in the Alerta AlertNode, thanks @nermolaev!
 - [#2409](https://github.com/influxdata/kapacitor/pull/2409): Optionally use kapacitor alert details as opsgenie description text,  thanks @JamesClonk!
+- [#2441](https://github.com/influxdata/kapacitor/pull/2441): Preallocate GroupIDs for increased performance by reducing allocations.
 
 ## v1.5.7 [2020-10-27]
 

models/point.go

@@ -87,6 +87,20 @@ func ToGroupID(name string, tags map[string]string, dims Dimensions) GroupID {
 		return NilGroup
 	}
 	var buf strings.Builder
+	l := 0
+	if dims.ByName {
+		// add capacity for the name + "\n"
+		l += len(name) + 1
+	}
+	for i, d := range dims.TagNames {
+		if i != 0 {
+			// add capacity for the comma after the tagnames
+			l++
+		}
+		// add capacity for the name length, and the tag length, and the "="
+		l += len(d) + len(tags[d]) + 1
+	}
+	buf.Grow(l)
 	if dims.ByName {
 		buf.WriteString(name)
 		// Add delimiter that is not allowed in name.