Re: CEPH Erasure Encoding + OSD Scalability

[Loic Dachary <loic@dachary.org>]

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[re-adding ceph-devel to the cc]

On 26/09/2013 20:36, Andreas-Joachim Peters wrote:> Hi Loic,
> today I forked he CEPH repository and will commit my changes to my GitHub fork asap ... (I am not familiar with GitHub in particular).
> I was finalizing the minimim_to_decode function today with test cases (it is more sophisticated in this case ...) ... I didn't fully get what the 'with cost' function is supposed to do diffrent from the one without cost?

I'd be happy to explain if 
https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodeInterface.h#L131
is unclear. Would you be so kind as to tell me what is confusing in the description ? 

> 
> 
> Cheers Andreas.
> 
> On Wed, Sep 25, 2013 at 8:48 PM, Loic Dachary <loic@dachary.org <mailto:loic@dachary.org>> wrote:
> 
> 
> 
>     On 25/09/2013 20:33, Andreas Joachim Peters wrote:> Yes, sure. I actually thought the same in the meanwhile ...  I have some questions:
>     >
>     > Q: Can/should it stay in the framework of google test's or you would prefer just a plain executable ?
>     >
> 
>     A plain executable would make sense. An simple example from src/test/Makefile.am :
> 
>     ceph_test_trans_SOURCES = test/test_trans.cc
>     ceph_test_trans_LDADD = $(LIBOS) $(CEPH_GLOBAL)
>     bin_DEBUGPROGRAMS += ceph_test_trans
> 
> 
>     > I have added local parity support to your erasure class adding a new argument: "erasure-code-lp" and
>     > two new methods:
>     >
>     > localparity_encode(...)
>     > localparity_decode(...)
>     >
>     > I made a more complex benchmark of (8,2) + 2 local parities (1^2^3^4, 5^6^7^8) which benchmarks performance of encoding/decoding as speed & effective write-latency for three cases (each for liberation & cauchy_good codecs):
>     >
>     > 1 (8,2)
>     > 2 (8,2,lp=2)
>     > 3 (8,2,lp=2) + crc32c (blocks)
>     >
>     > and several failure scenarios ... single, double, triple disk failures. Probably the best is if I make all this parameters configurable.
> 
>     Great :-) Do you have a public git repository where I could clone this & give it a try ?
> 
>     > Q: For the local parity implementation .... shall I inherit from your erasure plugin and overwrite the encode/decode method or you would consider a patch to the original class?
> 
>     It is a perfect timing for a patch to the original class.
> 
>     > I have also a 128-bit XOR implementation for the local parities. This will work with new gcc's & clang compilers ...
>     >
>     > Q: Which compilers/platforms are supported by CEPH? Is there a minimal GCC version?
> 
>     You can see all supported platforms here:
> 
>     http://ceph.com/gitbuilder.cgi
> 
>     I don't think the GCC version shows in the logs but you can probably figure it out from the corresponding distribution.
> 
>     > Q: is there some policy restricting comments within code? In general I see very few or no comments within the code ..
> 
>     :-) The mon code tends to be more heavily commented than the osd code (IMO) but I'm not aware of any policy. When I feel the need to comment, I write a unit test. If the unit test is difficult, I tend to comment to clarify its purpose. The problem with comments is that they quickly become obsolete and/or misleading. That being said, I don't think anyone will object if you heavily comment your code.
> 
>     Cheers
> 
>     > Cheers Andreas.
>     >
>     >
>     >
>     >
> 
>     --
>     Loïc Dachary, Artisan Logiciel Libre
>     All that is necessary for the triumph of evil is that good people do nothing.
> 
> 

-- 
Loïc Dachary, Artisan Logiciel Libre
All that is necessary for the triumph of evil is that good people do nothing.


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