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Re: Using bitmaps to accelerate fetch and clone

From
Jeff King <peff@peff.net>
Date
Sep 27, 2012, 21:36 UTC
Message-ID
<20120927213602.GA12512@sigill.intra.peff.net>
In-Reply-To
<7vfw63p2wi.fsf@alter.siamese.dyndns.org>
On Thu, Sep 27, 2012 at 02:33:01PM -0700, Junio C Hamano wrote:
Show 10 quoted lines
> Jeff King <peff@peff.net> writes:
> 
> > So yeah, we would want to put the pack trailer sha1 into the
> > supplementary index file, and check that it matches when we open it.
> > It's a slight annoyance, but it's O(1).
> 
> Yes.  If I am not mistaken, that is exactly how an .idx file makes
> sure that it describes the matching .pack file (it has packfile
> checksum in its trailer).  Otherwise you can repack the same set of
> objects into a new .pack file and make existing .idx very confused.

Yeah. In theory you wouldn't name the new packfile into place without also generating a new index for it. But even if you do it right, there's a race condition, and checking the trailer sha1 at least lets us know that they don't match (I assume we just reject the index, then; I guess this can result in an operation failing, but in practice it doesn't really happen, as we don't bother packing unless there are actually new objects).

-Peff
Previous: Junio C HamanoNext: David Michael Barr
Message 12 of 20 in “Using bitmaps to accelerate fetch and clone”
  1. Shawn PearceSep 27, 2012
  2. Nguyen Thai Ngoc DuySep 27, 2012
  3. Shawn PearceSep 27, 2012
  4. Nguyen Thai Ngoc DuySep 28, 2012
  5. Jeff KingSep 27, 2012
  6. Shawn PearceSep 27, 2012
  7. Jeff KingSep 27, 2012
  8. Shawn PearceSep 27, 2012
  9. Jeff KingSep 27, 2012
  10. Jeff KingSep 27, 2012
  11. Junio C HamanoSep 27, 2012
  12. Jeff KingSep 27, 2012
  13. David Michael BarrSep 27, 2012
  14. Nguyen Thai Ngoc DuySep 28, 2012
  15. Nguyen Thai Ngoc DuySep 28, 2012
  16. Shawn PearceOct 1, 2012
  17. Nguyen Thai Ngoc DuyOct 1, 2012
  18. Shawn PearceOct 1, 2012
  19. Nguyen Thai Ngoc DuyOct 1, 2012
  20. Shawn PearceOct 2, 2012

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