---------- Forwarded Message ---------- Subject: Re: Repository format comparison Date: Wednesday 15 November 2006 16:01 From: Matt Mackall <mpm@xxxxxxxxxxx> To: Giuseppe Bilotta <bilotta78@xxxxxxxxxx> Cc: mercurial@xxxxxxxxxxx On Wed, Nov 15, 2006 at 08:59:06PM +0100, Giuseppe Bilotta wrote: > Hello, on another mailing list I just found a link to this blog > article > > http://keithp.com/blog/Repository_Formats_Matter.html > > (from a month ago) which also has a brief mentioning of Mercurial: > > """ > Mercurial uses a truncated forward delta scheme where file revisions > are appended to the repository file, as a string of deltas with > occasional complete copies of the file (to provide a time bound on > operations). This suffers from two possible problems???the first is > fairly obvious where corrupted writes of new revisions can affect old > revisions of the file. Mercurial files are append-only. New revisions (corrupted or not), do not affect old revisions. If a hardware or operating system bug causes a write to scribble over the wrong part of a file, all bets are off of course. But such bugs could just as easily scribble over any other part of the disk, so I think this is no more of an issue than it is for any other possible system. > The second is more subtle -- system failure during commit will leave > the file contents half written. Mercurial has recovery techniques to > detect this, but they involve truncating existing files, a piece of > the Linux kernel which has constantly suffered from race conditions > and other adventures. Constantly is rather overstating it. There have been a few interesting truncate races found and sorting out one of them was a process that took several months a few years back. But none are the sort that affect the average application and none are the sort that would manifest with the very straightforward usage of truncate in Mercurial. -- Mathematics is the supreme nostalgia of our time. _______________________________________________ Mercurial mailing list Mercurial@xxxxxxxxxxx http://selenic.com/mailman/listinfo/mercurial ------------------------------------------------------- -- Jesse Keating Release Engineer: Fedora
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