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Write sparse files in restorer

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This writes files by using (*os.File).Truncate, which resolves to the
truncate system call on Unix.

Compared to the naive loop,

	for _, b := range p {
		if b != 0 {
			return false
		}
	}

the optimized allZero is about 10× faster:

name       old time/op    new time/op     delta
AllZero-8    1.09ms ± 1%     0.09ms ± 1%    -92.10%  (p=0.000 n=10+10)

name       old speed      new speed       delta
AllZero-8  3.84GB/s ± 1%  48.59GB/s ± 1%  +1166.51%  (p=0.000 n=10+10)
This commit is contained in:
greatroar
2020-02-26 21:48:05 +01:00
committed by Michael Eischer
parent b48766d7b8
commit 5d4568d393
4 changed files with 171 additions and 17 deletions
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4
internal/restorer/fileswriter_test.go
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@@ -18,19 +18,15 @@ func TestFilesWriterBasic(t *testing.T) {
rtest.OK(t, w.writeToFile(f1, []byte{1}, 0, 2))
rtest.Equals(t, 0, len(w.buckets[0].files))
rtest.Equals(t, 0, len(w.buckets[0].users))
rtest.OK(t, w.writeToFile(f2, []byte{2}, 0, 2))
rtest.Equals(t, 0, len(w.buckets[0].files))
rtest.Equals(t, 0, len(w.buckets[0].users))
rtest.OK(t, w.writeToFile(f1, []byte{1}, 1, -1))
rtest.Equals(t, 0, len(w.buckets[0].files))
rtest.Equals(t, 0, len(w.buckets[0].users))
rtest.OK(t, w.writeToFile(f2, []byte{2}, 1, -1))
rtest.Equals(t, 0, len(w.buckets[0].files))
rtest.Equals(t, 0, len(w.buckets[0].users))
buf, err := ioutil.ReadFile(f1)
rtest.OK(t, err)