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Re: Slow ISVNClient.getChangelists on Linux/NFS share

From: Branko Čibej <brane_at_apache.org>
Date: Thu, 19 Oct 2017 09:05:09 +0200

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.

-- Brane
Received on 2017-10-19 09:05:14 CEST

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