Explicitly reallocate slice to avoid up to 2x overhead

bboreham · bboreham · commit a2ec1918a074 · 2019-09-27T06:42:15.000Z
Signed-off-by: Bryan Boreham &lt;bryan@weave.works&gt;
diff --git a/pkg/chunk/encoding/bigchunk.go b/pkg/chunk/encoding/bigchunk.go
@@ -65,6 +65,12 @@ func (b *bigchunk) addNextChunk(start model.Time) error {
 		}
 	}
 
+	// Explicitly reallocate slice to avoid up to 2x overhead if we let append() do it
+	if len(b.chunks)+1 > cap(b.chunks) {
+		newChunks := make([]smallChunk, len(b.chunks), len(b.chunks)+1)
+		copy(newChunks, b.chunks)
+		b.chunks = newChunks
+	}
 	b.chunks = append(b.chunks, smallChunk{
 		XORChunk: *chunkenc.NewXORChunk(),
 		start:    int64(start),

Original file line number	Diff line number	Diff line change
`@@ -65,6 +65,12 @@ func (b *bigchunk) addNextChunk(start model.Time) error {`
`65`	`65`	`}`
`66`	`66`	`}`
`67`	`67`
	`68`	`+ // Explicitly reallocate slice to avoid up to 2x overhead if we let append() do it`
	`69`	`+ if len(b.chunks)+1 > cap(b.chunks) {`
	`70`	`+ newChunks := make([]smallChunk, len(b.chunks), len(b.chunks)+1)`
	`71`	`+ copy(newChunks, b.chunks)`
	`72`	`+ b.chunks = newChunks`
	`73`	`+ }`
`68`	`74`	`b.chunks = append(b.chunks, smallChunk{`
`69`	`75`	`XORChunk: *chunkenc.NewXORChunk(),`
`70`	`76`	`start: int64(start),`