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From Kyle Leber <kyle.le...@gmail.com>
Subject Re: svn merge operation extremely slow
Date Sat, 01 Oct 2011 23:33:10 GMT
What method of profiling do you recommend?  I have used gprof previously
(it's been awhile) but am not familiar with the subversion project source
code and build setup.  Is the a online guide or wiki describing the
preferred setup for performing this?

Kyle

On Sat, Oct 1, 2011 at 3:10 PM, Daniel Shahaf <d.s@daniel.shahaf.name>wrote:

> Johan Corveleyn wrote on Sat, Oct 01, 2011 at 20:47:29 +0200:
> > [ Please do not top-post on this list, i.e. please put your reply
> > below or inline. More below ... ]
> >
> > On Sat, Oct 1, 2011 at 6:49 PM, Kyle Leber <kyle.leber@gmail.com> wrote:
> > > On Fri, Sep 30, 2011 at 7:15 PM, Johan Corveleyn <jcorvel@gmail.com>
> wrote:
> > >>
> > >> On Fri, Sep 30, 2011 at 3:29 PM, Kyle Leber <kyle.leber@gmail.com>
> wrote:
> > >> > I've encountered what I think is a problem with subversion, but I'm
> not
> > >> > completely sure (and according to the online instructions I should
> bring
> > >> > it
> > >> > up here prior to filing a bug).
> > >>
> > >> Actually, the instructions on
> > >> http://subversion.apache.org/issue-tracker.html say that you should
> > >> send your report to users@, not dev@. So I'm adding users@. Please
> > >> drop dev@ from any further replies.
> > >>
> > >> > Basically, we're trying to merge a rather large collection of
> > >> > fixes back in our trunk.  I check out a fresh copy of the trunk,
> > >> > then use the merge syntax: svn merge https://path/to/my/branch .
> > >> >
> > >> > This generally churns along just fine, but we occasionally get
> > >> > hung up on medium sized binary files where the svn client jumps
> > >> > to 100% cpu usage and sits on it for 3+ hours before moving on to
> > >> > the next file.  These files are anywhere from 3-10MB in size, so
> > >> > not ridiculously huge.  We generally have these files marked as
> > >> > octet stream, but changing to text did not help the situation
> > >> > when we tried that.
> > >> >
> > >> > I did find an old forum discussion about a potential issue that
> > >> > could be related.  I was wondering if this was ever addressed and
> > >> > could it still be the same problem.  Link is here:
> > >> > http://www.svnforum.org/threads/36123-Slow-SVN-merge
> > >> >
> > >> > I'm using svn client 1.6.12.  I looked at the online change log
> > >> > up through the 1.7 alphas and didn't see any bug fixes that
> > >> > sounded relevant.
> > >>
> > >> This could be a relevant change (listed in the 1.7 release notes, not
> > >> in the change log):
> > >>
> > >>
> http://subversion.apache.org/docs/release-notes/1.7.html#diff-optimizations
> > >>
> > >> Can you please try one of the 1.7 pre-release binaries, and see if it
> > >> helps? See http://subversion.apache.org/packages.html#pre-release
> > >>
> > > Thanks, Johan.  I tested with 1.7rc4 and it did not make any
> perceptible
> > > difference.  Anything else I can try?
> >
> > Hm, that's unfortunate.
> >
> > Actually, it was to be expected that this wouldn't help, because the
> > diff-optimizations in 1.7 only play a role when merging text files
> > (and diffing and blaming). And you said those
> > "files-that-make-merge-hang" are generally marked as octet-stream, and
> > changing them to text made no difference.
> >
> > That seems to indicate that the 100% cpu usage on the client isn't
> > spent in the diff code (unlike the forum thread that you linked to,
> > where the poster tracked it down to libsvn_diff/lcs.c --- he would
> > definitely have been helped by the 1.7 improvements).
> >
>
> What does 'svn merge' do for binary files?  I checked svn_wc__merge()
> a few months ago and for binary files all it knew to do was
>
> (a) if mine == merge-left then set merged := merge-right
> (b) invoke the configured diff3-cmd
> (c) raise a conflict
>
> but it didn't do any line-based merge (per Johan's second response).
>
> > So there's another reason. Maybe it has something to do with (lots of)
> > subtree mergeinfo? Can you verify if there is a lot of svn:mergeinfo
> > on directories and files all over the place?
> >
> > Also: can you tell us what version is running on the server?
> >
> > Maybe other people on this list have had similar experiences, and can
> > give some suggestions?
> >
>
> Another line of thought: the algorithm for computing binary deltas
> changed a few years ago, and I recall reading (on old bug reports?)
> about some cases in which the delta combiner would be inefficient for
> deltas generated by old servers --- i.e., it would be expensive to 'svn
> cat' files that were committed to old servers in repositories that
> haven't been dumped/loaded by a newer server.
>
> In any case: can you run the merge under a profiler and tell us in what
> function(s) time is spent?
>
> Daniel
>
> > --
> > Johan
>

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