Re: Will the number of objects that have ever existed be infinite?

[Wido den Hollander <wido@42on.com>]

On 05/23/2015 08:58 AM, 李沛伦 wrote:
> Hello!
> 
> I'm a GSoC student this year and my job is to introduce Missing Rate
> Curve (or reuse distance exactly) of objects into OSD. Now I'm trying
> to find a proper algorithm to implement but there is a problem: Should
> I take the number of objects tracked in an OSD as infinite or
> constant?
> 

A OSD doesn't track on a per-object basis, but it keeps track of
Placement Groups (PGs). A OSD can have a X number of PGs.

Technically the number of PGs might be infinite, but in practice you are
bound to CPU and Memory limits.

So I would be careful with the word "infinite", since nothing is really
infinite, eg size of a int/long might be the limitation for something.

But in theory there is no object or PG limit per OSD.

> The point is that there is an algorithm that use hash to sample only
> constant number of references to do the analysis and is proved to be
> accurate, which makes it possible to do online MRC construction. That
> accuracy is supported by the fact that the memory addresses is
> bounded, while objects can be deleted and created again and again in
> Ceph. Is is reasonable to think that an OSD only serves bounded number
> of objects in its life time (or the time period that we want to
> compute MRC)?
> 
> Any other comment about this project is also welcomed :)
> 


-- 
Wido den Hollander
42on B.V.
Ceph trainer and consultant

Phone: +31 (0)20 700 9902
Skype: contact42on
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