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Re: fs-rep-sharing branch

From: Erik Huelsmann <ehuels_at_gmail.com>
Date: Wed, 22 Oct 2008 13:44:18 +0200

On Wed, Oct 22, 2008 at 1:28 PM, Greg Stein <gstein_at_gmail.com> wrote:
> On Wed, Oct 22, 2008 at 3:13 AM, Erik Huelsmann <ehuels_at_gmail.com> wrote:
>> On Wed, Oct 22, 2008 at 11:12 AM, Listman <listman_at_burble.net> wrote:
>>>
>>> On Oct 22, 2008, at 12:42 AM- Oct 22, 2008, Ivan Zhakov wrote:
>>>
>>>> On Wed, Oct 22, 2008 at 10:29 AM, David Glasser
>>>> <glasser_at_davidglasser.net> wrote:
>>>>>
>>>>> On Tue, Oct 21, 2008 at 9:39 PM, Listman <listman_at_burble.net> wrote:
>>>>>>
>>>>>> On Oct 21, 2008, at 8:05 PM- Oct 21, 2008, Greg Stein wrote:
>>>>>>
>>>>>>> After you've changed the editor API, the wc_entry_t structure,
>>>>>>> migrated all old clients over to svn_checksum_t, and then switched the
>>>>>>> storage defaults over to sh1, *then* we can talk about "an easy
>>>>>>> switch".
>>>>>>>
>>>>>>> The simple fact is that we're going to be running around with md5
>>>>>>> checksums in hand for a long while. OR we double-compute, and I'm not
>>>>>>> willing to burn that much CPU to satisfy somebody's misguided
>>>>>>> preconception about md5 collisions. And double-compute generally means
>>>>>>> that we *carry around* both checkums. You wanna update all the APIs
>>>>>>> for that, too?
>>>>>>>
>>>>>>
>>>>>> +1 (on gregs position for this issue)
>>>>>>
>>>>>> lets not introduce more performance overheads based on a corner case.
>>>>>>
>>>>>> svn as it stands is way toooo slooow folks... please don't get
>>>>>> distracted
>>>>>> from
>>>>>> that fact. i'm dealing with 20 minutes commits, 15 minute status checks
>>>>>> etc
>>>>>> and my
>>>>>> users want to know why...
>>>>>>
>>>>>> also, svn already does way too many checksums from what i've been able
>>>>>> to
>>>>>> decipher.
>>>>>
>>>>> Well, if all you care about is speed, then revert the fsfs rep-sharing
>>>>> code entirely... it makes FSFS strictly less correct and presumably
>>>>> strictly slower, bringing only a space benefit which (for FSFS)
>>>>> appears to not be that large.
>>>>>
>>>> I agree with David: Subversion reliability is much more important than
>>>> speed. Also I do not understand why we so care about disk space for
>>>> repository: disk space is very cheap and become cheaper every day.
>>>> Think that priority list should be:
>>>> - Reliability
>>>> - Speed (CPU/memory usage)
>>>> - Disk space
>>>
>>>
>>>
>>> with todays SVN performance anyone with a need for centralized DM and large
>>> data-sets would be better off using P4.
>>>
>>> If SVN isn't reliable we lose, but if SVN is so slow that users aren't
>>> efficient and
>>> get frustrated we still lose.
>>
>> We acknowledge speed problems on the client side. Do we have speed
>> problems on the server, though, is the question: some of the speed
>> problems on the client are being addressed.
>
> Actually, it is more pronounced on the server since it is shared
> across many clients. Profiling tests of an svn server show that it
> spends its time in two operations: computing deltas, and computing
> checksums. An svn server is generally CPU-bound rather than IO-bound.
> Planning for capacity requires monitoring of the CPU and adding more
> servers well before worrying about overloading a storage system.

Ah. Valuable info. Thanks. I have such low loads I'm not noticing
this. However, for the people I was talking about, this doesn't matter
much: they don't need to pay for the server. It's (to them) just an
exponent of a system (and an approach). It's an argument to put
against it.

BTW: The OP compared with p4; in order to get a fair comparison, I
think the comparison should be made on the same hardware, each with
their own proprietary protocol and their respective authn+authz
systems. It would be unfair to compair p4-over-its-protocol with
svn-over-http.

> So yeah. We *do* have speed problems on the server.
Thanks.

Bye,

Erik.

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Received on 2008-10-22 13:44:34 CEST

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