Transaction semantics

[Neil Moore <ne...@adobe.com>]

Does a curator transaction isolate me from changes in the underlying data? E.g. if I do


CuratorTransaction transaction = curator.inTransaction();

curator.getChildren().forPath(entityPath);

curator.getData()...

etc.


will forPath() and getData() operate on the same underlying data irrespective of concurrent modifications elsewhere?

If not, can I achieve a consistent read of all the data in a path by some other means?

Thanks

Neil

Re: Transaction semantics

[Jordan Zimmerman <jo...@jordanzimmerman.com>]

Curator's transaction is a wrapper around the normal ZooKeeper transaction feature. The ZK docs are not great on this: https://zookeeper.apache.org/doc/r3.4.6/api/org/apache/zookeeper/ZooKeeper.html#multi(java.lang.Iterable) <https://zookeeper.apache.org/doc/r3.4.6/api/org/apache/zookeeper/ZooKeeper.html#multi(java.lang.Iterable)>

The TL;DR is that a ZooKeeper "transaction" is a set of batch modifications that are committed as one transaction (via 1 API call). It's nothing like an RDBMS transaction so your example won't work. 
> If not, can I achieve a consistent read of all the data in a path by some other means?

ZooKeeper is an eventually consistent system. It is not possible to achieve RDBMS levels of consistency. ZK clients can potentially read old data if the instance you are connected to hasn't yet been updated. Further, I'd say that ZK is not a data store. It's a distributed consistency manager. If you are looking for a consistent (or semi-consistent) key-value store you should use a different technology.
-Jordan

> On Mar 22, 2017, at 1:20 AM, Neil Moore <ne...@adobe.com> wrote:
> 
> Does a curator transaction isolate me from changes in the underlying data? E.g. if I do
> 
> CuratorTransaction transaction = curator.inTransaction();
> curator.getChildren().forPath(entityPath);
> curator.getData()...
> etc.
> 
> will forPath() and getData() operate on the same underlying data irrespective of concurrent modifications elsewhere?
> If not, can I achieve a consistent read of all the data in a path by some other means?
> Thanks 
> Neil
>