2015-03-17 15:25 GMT+08:00 徐昕 <xuxinhfut@xxxxxxxxx>: > Hi Alexandre, > > I have tried this out. It can improve the performance of rbd rollback > greatly when the difference between the image and the sanpshot is > small. > If the clone does not happen in the rollback process, you may consider it would properly happen when it is modified. I may agree, if one object is always not modified since the snapshot N, it may be treated as a cold object so that it is likely not to be modified in the following period. > But i'm not sure if this change may cause potential problem. > > Thanks > Xin Xu > > 2015-03-17 14:43 GMT+08:00 Alexandre DERUMIER <aderumier@xxxxxxxxx>: >> Hi, >> I'm not sure it's helping for snapshot rollback, but hammer have a new object_map feature: >> >> https://wiki.ceph.com/Planning/Blueprints/Hammer/librbd%3A_shared_flag,_object_map >> >> >> which help for resize,flatten,... >> >> >> ----- Mail original ----- >> De: "徐昕" <xuxinhfut@xxxxxxxxx> >> À: "ceph-devel" <ceph-devel@xxxxxxxxxxxxxxx> >> Envoyé: Mardi 17 Mars 2015 04:24:28 >> Objet: Can i improve the performance of rbd rollback in this way？ >> >> Hi, >> >> I am a newbie to ceph. Recently i need to improve the performance of >> rbd rollback on xfs in my project. Through experiment i found that the >> mechanism of rbd rollback is like this: >> >> When a image is rolled back to one of its snapshot (say N), for every >> object that has been allocated, >> case A) if the object has no snap version since snap N, then the head >> version will be copied back to the latest snap (say N+M); >> case B) if the object has snap version since snap N, and it has the >> latest snap version (N+M), then the oldest snap version since snap N >> (say N+x, 0<=x<=M) will be copied to cover the head version; >> case C) if the object has snap version since snap N, and it has no >> version in the latest snap (N+M), then the head version will be copied >> back to the latest snap N+M, and the oldest snap version since snap N >> (say N+x, 0<=x<M) will be copied to cover the head version. >> >> I think in case A, we need not to copied the head version back. So for >> improving performance, i comment the following statement in function >> ReplicatedPG::_rollback_to in osd/ReplicatedPG.cc, >> >> ...... >> else if (rollback_to->obs.oi.soid.snap == CEPH_NOSNAP) { >> // rolling back to the head; we just need to clone it. >> // ctx->modify = true; >> } >> ...... >> >> Can i improve performance of rollback like this? If CAN NOT, what is the reason? >> >> Thank you. >> >> Xin Xu >> -- >> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
