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Re: Slow ISVNClient.getChangelists on Linux/NFS share

From: Branko Čibej <brane_at_apache.org>
Date: Thu, 19 Oct 2017 10:23:09 +0200

On 19.10.2017 10:07, Thomas Singer wrote:
> On 2017-10-19 9:05, Branko Čibej wrote:
>> On 19.10.2017 08:30, Thomas Singer wrote:
>>> On 18.10.2017 19:56, Branko Čibej wrote:
>>>> On 18.10.2017 13:31, Thomas Singer wrote:
>>>>> Hi,
>>>>> When performing following steps on my old Linux test machine (with
>>>>> slow hard disk):
>>>>> - have a SVN working copy at /home/user/test
>>>>> - sudo apt install nfs-kernel-server
>>>>> - add following line to /etc/exports:
>>>>>     /home/user/test *(rw,sync,no_root_squash)
>>>>> - start the NFS server:
>>>>>     sudo systemctl start nfs-kernel-server.service
>>>>> - mount the NFS share:
>>>>>     sudo mount localhost:/home/user/test /home/user/test.nfs
>>>>> and then open /home/user/test.nfs in SmartSVN 9.2 (using SVN 1.9
>>>>> JavaHL binaries), adding/removing a file is very slow. It boils down
>>>>> to the call ISVNClient.getChangelists which takes ~8s on the NFS
>>>>> share
>>>>> (/home/user/test.nfs). First, I thought, it would be caused by the
>>>>> native-Java overhead calling the call-back ~11,000 times for my
>>>>> working copy, but when using the working copy directly
>>>>> (/home/user/test), the method just takes <1s though the ~11,000 times
>>>>> call-back invocations are still there.
>>>>> My working copy has no local modifications, no untracked or ignored
>>>>> files, no changelists.
>>>>> Is it expected that this method (ISVNClient.getChangelists) is so
>>>>> slow
>>>>> on a NFS share even if there are no changelists?
>>>> I don't know if it's "expected" but I bet that NFS is killing SQLite
>>>> performance.
>>>> https://www.mail-archive.com/sqlite-users@mailinglists.sqlite.org/msg88989.html
>>>> I'm not sure about the reason but the most likely answer, apart from
>>>> slow data rate and latency when compared to a local filesystem (which,
>>>> in your case on loopback, should not be an issue), is that the OS
>>>> can't
>>>> really use a cache for files on NFS since it has no way to know
>>>> whether
>>>> or not it's valid. With a lot of random-access reads and writes, that
>>>> can be a HUGE slowdown, as you found.
>>>> Also this:
>>>> https://sqlite.org/faq.html#q5
>>>> In other words, Subversion working copies on NFS are, and have always
>>>> been, a bad idea; not only because of SQLite but also because
>>>> Subversion's code itself relies on atomic renames, which NFS does not
>>>> provide.
>>>> -- Brane
>>> What SVN command (on command line) I should test to get a similar
>>> result as from ISVNClient.getChangelists?
>> If "adding/removing a file" is any indication, then "svn add" or "svn
>> remove" should be comparable.
> Sorry, this was misleading. Adding/removing a file cause a refresh of
> which ISVNClient.getChangelists takes the longest time. With SmartSVN
> Foundation ISVNClient.getChangelists is not invoked and hence much
> faster when refreshing after a command, e.g. add or remove.
> Which is the SVN command line equivalent of ISVNClient.getChangelists?

The only one I can find that actually uses the
svn_client_get_changelists() function is 'svn update --changelist', but
of course it also does an update, so the comparison is not entirely valid.

-- Brane
Received on 2017-10-19 10:23:16 CEST

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