RHQ 4.8 introduced the new Cassandra backend for metrics. There has been a tremendous amount of work since then focused on the management of the new RHQ Storage Node. We do want to impose on users the burden of managing a second database. One of our key goals is to provide robust management such that Cassandra is nothing more than an implementation detail for users.
The version of Cassandra shipped in RHQ 4.8 includes some native libraries. One of the main uses for those native libraries is compression. If the platform on which Cassandra is running has support for the native libraries, table compression will be enabled. Data files written to disk will be compressed.
All of the native libraries have been removed from the version of Cassandra shipped in RHQ 4.9. The reason for this change is to ensure RHQ continues to provide solid cross-platform support. The development and testing teams simply do not have the bandwidth right now to maintain native libraries for all of the supported platforms in RHQ and JON.
The following information applies only to RHQ 4.8 installs.
Since RHQ 4.9 does not ship with native those compression libraries, Cassandra will not be able to decompress the data files on disk.
Compression has to be disabled in your RHQ 4.8 installation before upgrading to 4.9. There is a patch which you will need to run prior to upgrading. Download rhq48-storage-patch.zip and follow the instructions provided in rhq48-storage-patch.sh|bat.
I do want to mention that we will likely re-enable compression using a pure Java compression library in a future RHQ release.