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. > >>>> > >>> > >> > >
