Re: Hitchhiker erasure code

[Loic Dachary <loic@dachary.org>]

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On 20/03/2015 13:37, Andreas Joachim Peters wrote:
> Hi Loic, 
> I looked at that some time ago.
> 
> Table 1 in the paper says it all:
> 
> If you care about decoding and reconstruction of data it gives a good improvement.
> If you care mainly about encoding speed, it is not the optimal choice (+72.1%).
> 
> The algorithm optimizes the reconstruction of data units. This is relevant if your read-size is typically smaller than the block-size e.g. you encode 4 MB objects and you read 4kb pages. With normal EC you get a read amplification of K*4k if a data stripe is down, while with hitchhiker you get only 2/3 of that traffic in case of (10,4).
> 
> The most interesting to implement is probably Hitchhiker-XOR+, which you have to combine with a Vandermonde matrix, it requires that the first parity is just the xor of all data chunks.
> 
> So, yes, there is certainly a benefit in implementing that compared to other approaches (Xorbas,LRC) since it does not involve a space overhead and opens the door to use larger K values and save space!
> 

That sounds appealing :-) Do you think it would be more relevant to implement this as an additional Ceph plugin ? Or as a new jerasure technique ?

-- 
Loïc Dachary, Artisan Logiciel Libre


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