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Re: FindFirstFile delay on merging resolved via profiling (r33447)

From: Erik Huelsmann <ehuels_at_gmail.com>
Date: Mon, 6 Oct 2008 20:57:12 +0200

On Mon, Oct 6, 2008 at 7:55 PM, Sander Rijken <sr_at_d-90.nl> wrote:
>>
>> This two line patch on svn_dirent_get_absolute is the result of several
>> hours of profiling and it makes the merge test we profiled 30% faster. (It
>> probably increases the speed of many other subversion commands as well).
>>
>> This very Windows specific slowdown was added in r13 when the call to
>> _fullpath() from the Microsoft C++ library was replaced by the more generic
>> apr_filepath_merge.
>>
>> On all platforms except windows apr_filepath_merge can only make the path
>> absolute, but on Windows it also allows the flag APR_FILEPATH_TRUENAME that
>> actually verifies if the path exists by checking the exact casing of the
>> path and all its ancestors.
>>
>> !! It actually performs disk IO !!
>>
>> On a typical test merge:
>> svn merge -c 31121,31211,31733,31846,32497,32800,32836,32837,33156,33178
>> http://svn.collab.net/repos/svn/trunk F:\wc\1.5.x
>> (F:\wc\1.5.x = 1.5.x branch @33444)
>>
>> This svn_dirent_get_absolute involves several thousands of calls to
>> FindFirstFile, while only 22 files receive updates.
>>
>> Removing this flag shaves 7 seconds from the merge time on my quad core
>> pc.
>> When I run it on a local mirror of the subversion repository the
>> difference is well over 30%. (Over webdav most time is spent waiting on bits
>> to arrive from the USA)
>>
>
> Actually in the above merge example, 9 merges are performed (one of them has
> already been merged), and for each merge svn_sleep_for_timestamps is called
> (sleeping for 1.1 seconds)
> This means that going from 19 to 12 seconds, should actually be explained as
> going from 9 to 2 seconds, which is a far greater improvement.
>
> Do we need the sleep function to be called after merging every revision
> (most commands that call it only call it when they're finished)?

No, we need it only at the end.

Bye,

Erik.

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Received on 2008-10-06 20:57:27 CEST

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