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Re: Subversion 1.9.0-dev FSFS performance tests

From: Julian Foad <julianfoad_at_btopenworld.com>
Date: Mon, 7 Jul 2014 17:44:28 +0100

I should probably let Stefan answer this, but...

C. Michael Pilato wrote:
>> On 07.07.2014 17:07, C. Michael Pilato wrote:
>>> On 07/07/2014 10:58 AM, Ivan Zhakov wrote:
>>>> My technical opinion that FSFS7/log addressing is slower by design,
>>>> because it's doing more (read index, then read data instead of just
>>>> read data) and only caching makes them comparable on performance to
>>>> FSFS6 repositories.

Ivan, it sounds like you've missed the important part of the design. It's designed to do LESS work in total, not more, because the cost of using the index is outweighed by the savings that it enables. As I understand it, a large saving is gained by re-ordering the data on disk during packing; that's why packing is essentially a requirement.

>>> I'm coming into this kinda late and after two weeks of vacation, so
>>> please forgive me if I misunderstand the above, but is it true that
>>> FSFS7 requires some kind of non-trivial caching just to match FSFS6's
>>> performance?
>> Yup.
> May I then presume that for folks who have many repositories being
> hosted from a single server, FSFS7 will necessarily bring either a CPU
> performance hit (insufficient cache) or a RAM requirement/consumption
> hit (sufficient, ginormous cache)?  Or is the cache configuration
> perhaps per-server rather than per-repository?

C-Mike, my understanding is that F7 comprehensively beats F6 speed, by large factors around x1.5 and more, in the kind of scenarios it's designed for. Caching is an assumed part of the design. I don't know how much it needs for what scenarios, or what you mean by 'non-trivial' or 'ginormous', but probably not as much as you might be led to think. I suggest you first look at Stefan's recent-ish test results [1] and other recent threads.

The only concerns about speed are about scenarios where it doesn't match F6 speed. While many scenarios are faster, some are slower, especially with the currently-default small cache size. Ivan reported some such scenarios [2].

My general observation is that wider testing is needed to draw firm conclusions.

- Julian

[1] "Re: Current FSFS performance [RAW]" <http://svn.haxx.se/dev/archive-2014-07/0004.shtml>

[2] "Subversion 1.9.0-dev FSFS performance tests" <http://svn.haxx.se/dev/archive-2014-06/0065.shtml>
Received on 2014-07-07 18:45:01 CEST

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