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3 commits

Author SHA1 Message Date
Michael Eischer
a5ebd5de4b restorer: Fix race condition in partialFile.WriteAt 
The restorer can issue multiple calls to WriteAt in parallel. This can
result in unexpected orderings of the Truncate and WriteAt calls and
sometimes too short restored files.
 2022-09-24 21:39:39 +02:00
Michael Eischer
5b6a77058a Enable sparseness only conditionally 
We can either preallocate storage for a file or sparsify it. This
detects a pack file as sparse if it contains an all zero block or
consists of only one block. As the file sparsification is just an
approximation, hide it behind a `--sparse` parameter.
 2022-09-24 21:20:00 +02:00
greatroar
5d4568d393 Write sparse files in restorer 
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)
 2022-09-24 21:18:48 +02:00