From 03d23e6faa2afd526771331083eda0f1d0bb0d3b Mon Sep 17 00:00:00 2001
From: greatroar <@>
Date: Fri, 6 Mar 2020 09:18:38 +0100
Subject: [PATCH] Speed up blob sorting in internal/repository
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

name                    old time/op    new time/op    delta
SortCachedPacksFirst-8     208µs ± 3%     186µs ± 3%  -10.74%  (p=0.000 n=10+8)

name                    old alloc/op   new alloc/op   delta
SortCachedPacksFirst-8     213kB ± 0%     139kB ± 0%  -34.62%  (p=0.000 n=10+10)

name                    old allocs/op  new allocs/op  delta
SortCachedPacksFirst-8     1.03k ± 0%     1.03k ± 0%   -0.19%  (p=0.000 n=10+10)
---
 internal/repository/repository.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/internal/repository/repository.go b/internal/repository/repository.go
index cee36ace8..47cf4fb0a 100644
--- a/internal/repository/repository.go
+++ b/internal/repository/repository.go
@@ -116,6 +116,7 @@ type haver interface {
 }
 
 // sortCachedPacksFirst moves all cached pack files to the front of blobs.
+// It overwrites blobs.
 func sortCachedPacksFirst(cache haver, blobs []restic.PackedBlob) []restic.PackedBlob {
 	if cache == nil {
 		return blobs
@@ -126,7 +127,7 @@ func sortCachedPacksFirst(cache haver, blobs []restic.PackedBlob) []restic.Packe
 		return blobs
 	}
 
-	cached := make([]restic.PackedBlob, 0, len(blobs)/2)
+	cached := blobs[:0]
 	noncached := make([]restic.PackedBlob, 0, len(blobs)/2)
 
 	for _, blob := range blobs {