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From Johan Corveleyn <jcor...@gmail.com>
Subject Re: svn merge operation extremely slow
Date Mon, 03 Oct 2011 12:35:30 GMT
On Mon, Oct 3, 2011 at 2:16 PM, Kyle Leber <kyle.leber@gmail.com> wrote:
>
>
> On Mon, Oct 3, 2011 at 4:10 AM, Johan Corveleyn <jcorvel@gmail.com> wrote:
>>
>> [ Again: please don't top-post on this list. I'm moving your reply to
>> the bottom. More below ... ]
>>
>> On Mon, Oct 3, 2011 at 2:24 AM, Kyle Leber <kyle.leber@gmail.com> wrote:
>> > On Sun, Oct 2, 2011 at 8:10 PM, Daniel Shahaf <d.s@daniel.shahaf.name>
>> > wrote:
>> >>
>> >> Kyle Leber wrote on Sun, Oct 02, 2011 at 20:05:19 -0400:
>> >> > Johan,
>> >> >
>> >> > I did a little more digging.  There were a few different places where
>> >> > svn
>> >> > seems to get hung up so I ran the gprof report on just the first one
>> >> > (the
>> >> > merge takes hours otherwise).  In this particular case, svn prints
>> >> > out
>> >> > that
>> >> > it is merging from a small text file while it is hanging for more
>> >> > than a
>> >> > minute @ 100% CPU.  When I examine "lsof", however, it see it
>> >> > actually
>> >> > has a
>> >> > different file open.  This one is a large (15 MB) "binary" file.  It
>> >> > turns
>> >> > out this binary file did not have a property in the trunk (which I
>> >> > think
>> >> > means it's treated as text, right?).  But in the branch it was marked
>> >> > as
>> >> > octet stream.   So perhaps svn is doing a text-based diff on this
>> >> > binary
>> >> > file because it used to be incorrectly marked as text?
>> >> >
>> >>
>> >> If either side is marked as binary then svn will defer to the "Use
>> >> merge-right if merge-left == base, else conflict" algorithm.
>> >>
>> >> Could you share the value of 'svn proplist --verbose' on both files?
>> >>
>> > Yup, trunk version has empty properties
>> > branch version has:
>> >
>> > svn:mime-type
>> >     application/octet-stream
>> >
>>
>> What is the merge target? Is it a trunk working copy (the one without
>> mime-type), or a branch working copy (with
>> svn:mime-type=application/octet-stream)?
>>
>> I think it's the mime-type of the merge target that determines if
>> merge will take the "binary" route, or the "text" route. See this
>> snippet from libsvn_wc/merge.c [1] (in the function
>> svn_wc__internal_merge):
>>
>> [[[
>>  /* Decide if the merge target is a text or binary file. */
>>  if ((mimeprop = get_prop(&mt, SVN_PROP_MIME_TYPE))
>>      && mimeprop->value)
>>    is_binary = svn_mime_type_is_binary(mimeprop->value->data);
>>  else
>>    {
>>      const char *value = svn_prop_get_value(mt.actual_props,
>>                                             SVN_PROP_MIME_TYPE);
>>
>>      is_binary = value && svn_mime_type_is_binary(value);
>>    }
>> ]]]
>>
>> (mt is the merge target)
>>
>> I'm not terribly familiar with this part of the codebase. But on first
>> sight, this seems to say:
>>
>>  (1) Look at the mime-type of the "base version" of the merge target.
>> If that's binary, then we'll go binary.
>>
>>  (2) If the "base" of the merge target doesn't have a mime-type, look
>> if it has one on the "actual" node (the uncommitted local
>> modifications). If that's binary, then we'll go binary.
>>
>>  (3) Else: text merge
>>
>> So I'm guessing that you're merging to trunk, the target without
>> mime-type property, which makes svn take the "text" route for merging.
>> Is that correct?
>>
>> If that's the case, maybe you can simply set the mime-type on that
>> binary file in your merge target, as a local modification (I don't
>> think you need to even commit it). Can you try that?
>>
>> --
>> Johan
>>
>> [1]
>> http://svn.apache.org/repos/asf/subversion/trunk/subversion/libsvn_wc/merge.c
>
> Johan,
>
> Sorry for the top-post.  Hopefully this is better :)

Much better, thank you :).

> I set the mime-type to "application/octet-stream" in the working copy prior
> to merge and this fixed the problem.  No more heavy CPU usage or excessive
> time spent on the file.

I'm glad it helped. Apart from the performance, it's important that
svn does this merge the "binary way", because as you said line-based
merges are not correct for this file.

-- 
Johan

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