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Re: [PATCH 5/6] Allow to use crc32 as a lighter checksum on index

From
Dave Zarzycki <zarzycki@apple.com>
Date
Feb 7, 2012, 04:04 UTC
Message-ID
<159A2D07-0B02-4E85-B7AA-C668FDA9F382@apple.com>
In-Reply-To
<CAJo=hJvSyhv8EUh=6ROotc3Q=zQo7vbww_ShQJP3tf1T7s889g@mail.gmail.com>
On Feb 6, 2012, at 7:17 PM, Shawn Pearce <spearce@spearce.org> wrote:
Show 6 quoted lines
> I haven't really put a lot of thought into this. But I suspect CRC-32
> is sufficient on the index file, until it gets so big that the
> probability of a bit flip going undetected is too high due to the size
> of the file, but then we are into the "huge" index size range that has
> you trying to swap out SHA-1 for CRC-32 because SHA-1 is too slow. Uhm
> no.
CRCs are designed to be implemented in hardware and provide basic single-bit error checking for networking packets of disk blocks. With a good polynomial, they're reasonably effective at detecting a single-bit error within 8 or 16 kilobytes:
    http://www.ece.cmu.edu/~koopman/networks/dsn02/dsn02_koopman.pdf
Previous: Shawn PearceNext: Dave Zarzycki
Message 13 of 20 in “read-cache: use sha1file for sha1 calculation”
  1. 1/6 read-cache: use sha1file for sha1 calculationNguyễn Thái Ngọc Duy, Feb 6, 2012
  2. 2/6 csum-file: make sha1 calculation optionalNguyễn Thái Ngọc Duy, Feb 6, 2012
  3. 3/6 Stop producing index version 2Nguyễn Thái Ngọc Duy, Feb 6, 2012
  4. Junio C HamanoFeb 6, 2012
  5. Shawn PearceFeb 7, 2012
  6. Nguyen Thai Ngoc DuyFeb 7, 2012
  7. Nguyen Thai Ngoc DuyFeb 7, 2012
  8. Junio C HamanoFeb 7, 2012
  9. Thomas RastFeb 7, 2012
  10. 4/6 Introduce index version 4 with global flagsNguyễn Thái Ngọc Duy, Feb 6, 2012
  11. 5/6 Allow to use crc32 as a lighter checksum on indexNguyễn Thái Ngọc Duy, Feb 6, 2012
  12. Shawn PearceFeb 7, 2012
  13. Dave ZarzyckiFeb 7, 2012
  14. Dave ZarzyckiFeb 7, 2012
  15. 6/6 Automatically switch to crc32 checksum for index when it's too largeNguyễn Thái Ngọc Duy, Feb 6, 2012
  16. Dave ZarzyckiFeb 6, 2012
  17. Nguyen Thai Ngoc DuyFeb 6, 2012
  18. Dave ZarzyckiFeb 6, 2012
  19. Junio C HamanoFeb 6, 2012
  20. Nguyen Thai Ngoc DuyFeb 6, 2012

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