On 05/07/2013 02:53 PM, MORITA Kazutaka wrote: > Here is a simple scenario where sheep can show the old data: > > == > Epoch Nodes > 1 [A, B, C] <- A, B, and C has the object X > 2 [A, B, C, D] > 3 [A, B, C, D, E] > 4 [A, B, C, D, E, F] <- The object X are copied to D, E, and F, and > it is updated from X to X' at this epoch > 5 [A, B, C, D, E] > 6 [A, B, C, D] > 7 [A, B, C] <- D, E, and F have gone away at the same time at > epoch 4. > A, B, and C still have X and recover the object > to the working direcotry, but clients must see > X'. > == > > Currently, sheep rollbacks to the older epoch without considering the > consistency problem, so it can show the older data to clients. > > In the initial sheepdog codes, we returned SD_RES_EIO to clients when > we cannot guarantee that the object is the latest one. I'm not sure > which is the better approach now because the above example is unlikely > to happen and returning EIO can also stop VMs. To make sheepdog > tolerant against rapid node changes, I have come to think that we > should accept the consistency problem and print the error message > instead. >
Print the error message makes sense. But I don't understand the code yet. + case SD_RES_NO_OBJ: + /* + * No object means that there was no write success at + * this epoch. + */ + data_lost = false; + /* fall through */ So if A, B, C all return SD_RES_NO_OBJ, you set data_lost = false, in this case, we don't print an error, no? Thanks, Yuan -- sheepdog mailing list sheepdog@lists.wpkg.org http://lists.wpkg.org/mailman/listinfo/sheepdog
