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https://github.com/syncthing/syncthing.git
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b1c8f88a44
We've had weak/rolling hashing in the code for quite a while. It was a popular request for a while, based on the belief that rsync does this and we should too. However, the benefit is quite small; we save on average about 0.8% of transferred blocks over the population as a whole: <img width="974" alt="Screenshot 2025-03-28 at 17 09 02" src="https://github.com/user-attachments/assets/bbe10dea-f85e-4043-9823-7cef1220b4a2" /> This would be fine if the cost was comparably low, however the downside of attempting rolling hash matching is that we (by default) do a complete file read on the destination in order to look for matches before we starting pulling blocks for the file. For any larger file this means a sometimes long, I/O-intensive pause before the file starts syncing, for usually no benefit. I propose we simply rip off the bandaid and save the effort.
85 lines
1.8 KiB
Go
85 lines
1.8 KiB
Go
// Copyright (C) 2014 The Syncthing Authors.
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this file,
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// You can obtain one at https://mozilla.org/MPL/2.0/.
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package main
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import (
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"context"
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"flag"
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"log"
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"os"
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"path/filepath"
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_ "github.com/syncthing/syncthing/lib/automaxprocs"
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"github.com/syncthing/syncthing/lib/protocol"
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"github.com/syncthing/syncthing/lib/scanner"
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)
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func main() {
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log.SetFlags(0)
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log.SetOutput(os.Stdout)
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standardBlocks := flag.Bool("s", false, "Use standard block size")
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flag.Parse()
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path := flag.Arg(0)
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if path == "" {
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log.Fatal("Need one argument: path to check")
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}
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log.Println("File:")
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log.Println(" ", filepath.Clean(path))
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log.Println()
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fi, err := os.Lstat(path)
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if err != nil {
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log.Fatal(err)
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}
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log.Println("Lstat:")
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log.Printf(" Size: %d bytes", fi.Size())
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log.Printf(" Mode: 0%o", fi.Mode())
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log.Printf(" Time: %v", fi.ModTime())
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log.Printf(" %d.%09d", fi.ModTime().Unix(), fi.ModTime().Nanosecond())
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log.Println()
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if !fi.Mode().IsDir() && !fi.Mode().IsRegular() {
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fi, err = os.Stat(path)
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if err != nil {
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log.Fatal(err)
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}
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log.Println("Stat:")
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log.Printf(" Size: %d bytes", fi.Size())
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log.Printf(" Mode: 0%o", fi.Mode())
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log.Printf(" Time: %v", fi.ModTime())
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log.Printf(" %d.%09d", fi.ModTime().Unix(), fi.ModTime().Nanosecond())
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log.Println()
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}
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if fi.Mode().IsRegular() {
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log.Println("Blocks:")
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fd, err := os.Open(path)
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if err != nil {
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log.Fatal(err)
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}
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blockSize := int(fi.Size())
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if *standardBlocks || blockSize < protocol.MinBlockSize {
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blockSize = protocol.BlockSize(fi.Size())
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}
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bs, err := scanner.Blocks(context.TODO(), fd, blockSize, fi.Size(), nil)
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if err != nil {
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log.Fatal(err)
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}
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for _, b := range bs {
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log.Println(" ", b)
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}
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}
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}
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