N allocs -> 1 alloc -> bit faster still

taskset --cpu-list 5 go test -bench Benchmark . -benchmem
goos: linux
goarch: amd64
pkg: github.com/grafana/metrictank/mdata/cache
BenchmarkAddAsc         	 1000000	      1053 ns/op	     145 B/op	       3 allocs/op
BenchmarkAddDesc1       	   10000	   1456538 ns/op	   21720 B/op	       7 allocs/op
BenchmarkAddDesc4       	   10000	   1452870 ns/op	   21729 B/op	       9 allocs/op
BenchmarkAddDesc64      	    9984	   1449829 ns/op	   21700 B/op	       9 allocs/op
BenchmarkAddRangeAsc    	 3000000	       366 ns/op	     117 B/op	       0 allocs/op
BenchmarkAddRangeDesc4  	   10000	    363554 ns/op	    5503 B/op	       1 allocs/op
BenchmarkAddRangeDesc64 	   99968	    277954 ns/op	    3276 B/op	       0 allocs/op
PASS
ok  	github.com/grafana/metrictank/mdata/cache	84.321s

benchcmp post2.txt post3.txt
benchmark                   old ns/op     new ns/op     delta
BenchmarkAddAsc             1229          1053          -14.32%
BenchmarkAddDesc1           1454771       1456538       +0.12%
BenchmarkAddDesc4           1459969       1452870       -0.49%
BenchmarkAddDesc64          1453576       1449829       -0.26%
BenchmarkAddRangeAsc        945           366           -61.27%
BenchmarkAddRangeDesc4      363506        363554        +0.01%
BenchmarkAddRangeDesc64     278120        277954        -0.06%

benchmark                   old allocs     new allocs     delta
BenchmarkAddAsc             3              3              +0.00%
BenchmarkAddDesc1           7              7              +0.00%
BenchmarkAddDesc4           9              9              +0.00%
BenchmarkAddDesc64          9              9              +0.00%
BenchmarkAddRangeAsc        1              0              -100.00%
BenchmarkAddRangeDesc4      2              1              -50.00%
BenchmarkAddRangeDesc64     1              0              -100.00%

benchmark                   old bytes     new bytes     delta
BenchmarkAddAsc             145           145           +0.00%
BenchmarkAddDesc1           21720         21720         +0.00%
BenchmarkAddDesc4           21729         21729         +0.00%
BenchmarkAddDesc64          21700         21700         +0.00%
BenchmarkAddRangeAsc        137           117           -14.60%
BenchmarkAddRangeDesc4      5502          5503          +0.02%
BenchmarkAddRangeDesc64     3276          3276          +0.00%

Author: Dieterbe

mdata/cache/ccache_metric.go

@@ -86,6 +86,9 @@ func (mc *CCacheMetric) AddRange(prev uint32, itergens []chunk.IterGen) {
 	mc.Lock()
 	defer mc.Unlock()
 
+	// pre-allocate 1 slice, cheaper than allocating one by one
+	chunks := make([]CCacheChunk, 0, len(itergens))
+
 	// handle the first one
 	itergen := itergens[0]
 	ts := itergen.Ts
@@ -111,12 +114,13 @@ func (mc *CCacheMetric) AddRange(prev uint32, itergens []chunk.IterGen) {
 
 	// add chunk if we don't have it yet (most likely)
 	if _, ok := mc.chunks[ts]; !ok {
-		mc.chunks[ts] = &CCacheChunk{
+		chunks = append(chunks, CCacheChunk{
 			Ts:    ts,
 			Prev:  prev,
 			Next:  itergens[1].Ts,
 			Itgen: itergen,
-		}
+		})
+		mc.chunks[ts] = &chunks[len(chunks)-1]
 		if addKeysDirect {
 			mc.keys = append(mc.keys, ts)
 		}
@@ -130,12 +134,13 @@ func (mc *CCacheMetric) AddRange(prev uint32, itergens []chunk.IterGen) {
 		ts := itergen.Ts
 		// add chunk if we don't have it yet (most likely)
 		if _, ok := mc.chunks[ts]; !ok {
-			mc.chunks[ts] = &CCacheChunk{
+			chunks = append(chunks, CCacheChunk{
 				Ts:    ts,
 				Prev:  prev,
 				Next:  itergens[i+1].Ts,
 				Itgen: itergen,
-			}
+			})
+			mc.chunks[ts] = &chunks[len(chunks)-1]
 			if addKeysDirect {
 				mc.keys = append(mc.keys, ts)
 			}
@@ -162,12 +167,13 @@ func (mc *CCacheMetric) AddRange(prev uint32, itergens []chunk.IterGen) {
 
 	// add chunk if we don't have it yet (most likely)
 	if _, ok := mc.chunks[ts]; !ok {
-		mc.chunks[ts] = &CCacheChunk{
+		chunks = append(chunks, CCacheChunk{
 			Ts:    ts,
 			Prev:  prev,
 			Next:  next,
 			Itgen: itergen,
-		}
+		})
+		mc.chunks[ts] = &chunks[len(chunks)-1]
 		if addKeysDirect {
 			mc.keys = append(mc.keys, ts)
 		}