The multi operation *is* like a transaction. All the operations will succeed or none.
On Wed, Aug 14, 2019 at 9:33 AM Andor Molnar <[email protected]> wrote: > "it's said that ZooKeeper has a transaction mechanism” > > I’m still confused with this. ZooKeeper doesn’t support transactions to my > best knowledge. It has a `multi` operation feature, but that’s more like a > bulk operation, not transaction. > > "I want to tell ZooKeeper that the check and setData should be successful” > > I don’t think you can do that. ZK has no check-and-set support either. > > Maybe we should step back first and see what’s your use case exactly that > you’re trying to solve with ZooKeeper. I suspect that you’re trying to > follow the wrong approach or misusing ZooKeeper. > > Have you checked our tutorial and recipes page? > You can find some recommended usage patterns: > https://zookeeper.apache.org/doc/r3.5.5/recipes.html > https://zookeeper.apache.org/doc/r3.5.5/zookeeperTutorial.html > > If that’s not enough, you could also try Curator which has even more > built-in high level functionalities on top of basic ZK commands. > > Andor > > > > > On 2019. Aug 14., at 17:52, Zili Chen <[email protected]> wrote: > > > > Hi Andor, > > > > Thanks for your attention. > > > > The problem is that in concurrent scenario zk.setData() could still > failed > > if there is another thread delete the node. I know with proper lock > strategy > > and ownership separation this can be avoid but it's said that ZooKeeper > has > > a transaction mechanism so I'd like to see whether I can make use of it. > > > > There is where I turn to > > > > zk.multi(Op.check(path1), Op.setData(path2, data)); // path1 == or != > path2 > > is irrelevant > > > > when the existence of a mark node(path1) guarded a condition and I want > to > > make > > sure that setData successes only if the mark node exist. If I check the > > existence > > first and commit setData, a remove to the node could break the guard. In > > other > > words, I want to tell ZooKeeper that the check and setData should be > > successful > > committed or fail to be committed atomically. > > > > Best, > > tison. > > > > > > Andor Molnar <[email protected]> 于2019年8月14日周三 下午11:12写道： > > > >> Hi Zili, > >> > >> There’s no such functionality in ZooKeeper as far as I’m concerned. I > >> think your multi example (zk.multi(Op.check(path), Op.setData(path, > data))) > >> is already a usage pattern which multi is not designed to support. > >> > >> Why do you need to do this in “transactions” (there’s no transaction in > >> ZK)? > >> > >> In Java you can do: > >> > >> try { > >> zk.create(); > >> } catch (NodeExistsException e) { > >> // swallow exception > >> } > >> zk.setData(); > >> … > >> > >> Regards, > >> Andor > >> > >> > >> > >> > >>> On 2019. Aug 6., at 14:44, Zili Chen <[email protected]> wrote: > >>> > >>> Hi Enrico, > >>> > >>> Thanks for your reply. > >>> > >>>> In this case usually you use conditional setData, using the 'version' > of > >>>> thr znode > >>> > >>> > >>> what if the caller has no idea on whether the node exist?(see also > >>> my if-else pseudo-code above.) > >>> > >>> IIRC if we call `setData` on a non-exist path a NoNodeException > >>> will be thrown. > >>> Best, > >>> tison. > >>> > >>> > >>> Enrico Olivelli <[email protected]> 于2019年8月6日周二 下午8:27写道： > >>> > >>>> Il mar 6 ago 2019, 13:47 Zili Chen <[email protected]> ha scritto: > >>>> > >>>>> Any ideas? > >>>>> > >>>>> > >>>>> Zili Chen <[email protected]> 于2019年7月29日周一 上午11:12写道： > >>>>> > >>>>>> Hi ZooKeepers, > >>>>>> > >>>>>> Currently our transaction mechanism supports doing > >>>>>> create/setData/checkExist/delete in transaction. However, taking > this > >>>>>> scenario into consideration, we want to put data in path "/path" but > >>>>>> don't know whether the znode exists or not. Let's say we program as > >>>>>> below > >>>>>> > >>>>>> if (zk.exist(path)) { > >>>>>> zk.setData(path, data); > >>>>>> } else { > >>>>>> zk.create(path, data); > >>>>>> } > >>>>> > >>>> > >>>> Do you need to perform other ops in the same transaction? > >>>> In this case usually you use conditional setData, using the 'version' > of > >>>> thr znode > >>>> > >>>> > >>>> Enrico > >>>> > >>>>> > >>>>>> if we want to do the check and "put" in transaction, it would be > like > >>>>>> > >>>>>> zk.multi(Op.check(path), Op.setData(path, data)); > >>>>>> > >>>>>> but we cannot add a "else" branch. ZooKeeper's transaction would all > >>>>>> success or fail. > >>>>>> > >>>>>> Is there any way to do an "if-else" transaction? > >>>>>> > >>>>>> Best, > >>>>>> tison. > >>>>>> > >>>>> > >>>> > >> > >> > >
