After some lengthy discussion with Stefan, I think the migration tool needs to be run
while the server is offline or possibly in maintenance mode. The best time to run the tool
would be prior to running the RHQ installer. A problem with doing the data migration while
the server is running is that we could wind up with skews in the aggregate data. The
easiest and fastest way to ensure data is consistent for both pre- and post-upgrade is to
run the data migration while the server is down.
- John
On Jan 2, 2013, at 6:20 PM, Stefan Negrea <snegrea(a)redhat.com> wrote:
Hello Everybody,
With new Cassandra based metrics storage system, existing data will need to be migrated
out of existing SQL storage to Cassandra. I put together a simple design document for the
data migration tool that will be delivered with RHQ when the new metrics storage system is
completed.
My initial thoughts about the tool are:
1) Restartable migration process, this will be especially useful for users with large
amounts of metrics.
2) Favour robustness over performance because this migration will be done only once.
3) Make the tool external to the product (not part of the installation), so user can do
the migration ahead of the upgrade.
Here is the full design document:
https://docs.jboss.org/author/display/RHQ/Metrics+Data+Migration+-+Design
Feedback is more than welcomed since this tool is still in the early planning stages.
Thank you,
Stefan Negrea
Software Engineer
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