From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wido den Hollander Subject: Re: Will the number of objects that have ever existed be infinite? Date: Sat, 23 May 2015 10:55:38 +0200 Message-ID: <5560408A.5000906@42on.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from websrv.42on.com ([31.25.102.167]:46875 "EHLO websrv.42on.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750967AbbEWIzm (ORCPT ); Sat, 23 May 2015 04:55:42 -0400 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: =?UTF-8?B?5p2O5rKb5Lym?= , "ceph-devel@vger.kernel.org" On 05/23/2015 08:58 AM, =E6=9D=8E=E6=B2=9B=E4=BC=A6 wrote: > Hello! >=20 > 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: Shoul= d > I take the number of objects tracked in an OSD as infinite or > constant? >=20 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 ar= e 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 numbe= r > of objects in its life time (or the time period that we want to > compute MRC)? >=20 > Any other comment about this project is also welcomed :) >=20 --=20 Wido den Hollander 42on B.V. Ceph trainer and consultant Phone: +31 (0)20 700 9902 Skype: contact42on -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html