From 2e7d47502932dca7e3b04ee3959270045ad17280 Mon Sep 17 00:00:00 2001
From: Michael Eischer <michael.eischer@fau.de>
Date: Sat, 15 Aug 2020 17:41:55 +0200
Subject: [PATCH] Process packs in order of first appearance

---
 internal/restorer/filerestorer.go | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/internal/restorer/filerestorer.go b/internal/restorer/filerestorer.go
index 2dc5982b0..af6427a49 100644
--- a/internal/restorer/filerestorer.go
+++ b/internal/restorer/filerestorer.go
@@ -101,6 +101,10 @@ func (r *fileRestorer) forEachBlob(blobIDs []restic.ID, fn func(packID restic.ID
 func (r *fileRestorer) restoreFiles(ctx context.Context) error {
 
 	packs := make(map[restic.ID]*packInfo) // all packs
+	// Process packs in order of first access. While this cannot guarantee
+	// that file chunks are restored sequentially, it offers a good enough
+	// approximation to shorten restore times by up to 19% in some test.
+	var packOrder restic.IDs
 
 	// create packInfo from fileInfo
 	for _, file := range r.files {
@@ -123,6 +127,7 @@ func (r *fileRestorer) restoreFiles(ctx context.Context) error {
 					files: make(map[*fileInfo]struct{}),
 				}
 				packs[packID] = pack
+				packOrder = append(packOrder, packID)
 			}
 			pack.files[file] = struct{}{}
 		})
@@ -157,7 +162,8 @@ func (r *fileRestorer) restoreFiles(ctx context.Context) error {
 	}
 
 	// the main restore loop
-	for _, pack := range packs {
+	for _, id := range packOrder {
+		pack := packs[id]
 		select {
 		case <-ctx.Done():
 			return ctx.Err()