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The library currently has hardcoded the write consistency level to LOCAL_QUORUM. This means that in a three node DC, with replication factor 2, if one node is down it can't write. This hurts reliability, for a gain in consistency.

What do you think about defaulting to LOCAL_ONE instead? As far as I can see, the only drawback would be that it takes a little longer for the cluster to "agree" on the written data. But since there are never any changes to existing points, only new points added, there can't be any real inconsistencies. In the worst case, new data may seem missing for a short time. The gain would be higher performance, and handling node failures in small clusters better.

Of course, ideally, the consistency level should be configurable anyway :)

In the current version, the library is storing the event receive time and event insert time into the database.
It would be useful to add an option to be able to enable this feature only on-demand.
It appears that these timestamps do not seem to be very useful since the EventSubscriber is already monitoring the min and max processing time. Disabling this feature could help saving quite a lot of space.

We should add a copyright notice and a statement of copying permission, saying that the program is distributed under the terms of the GNU Lesser General Public License in every source file.

In the current version of HDB++ Event Subscriber and libhdb++cassandra library, a DB Storage error message is reported when there is a problem storing data into Cassandra, without more details about the error. Using exceptions in the library could help improving diagnostics for problems related to Cassandra storage.

It would be useful to be able to configure the logging level of the HDB++ Cassandra library (and Cassandra driver logging level) via LibConfiguration Tango property used by the HDBEventSubscriber and HDBConfigurationManager device servers.