[openstack-dev] [trove] datastore migration issues

Greg Hill greg.hill at RACKSPACE.COM
Thu Dec 19 15:25:35 UTC 2013

We did consider doing that, but decided it wasn't really any different from the other options as it required the deployer to know to alter that data.  That would require the fewest code changes, though.  It was also my understanding that mysql variants were a possibility as well (percona and mariadb), which is what brought on the objection to just defaulting in code.  Also, we can't derive the version being used, so we *could* fill it with a dummy version and assume mysql, but I don't feel like that solves the problem or the objections to the earlier solutions.  And then we also have bogus data in the database.

Since there's no perfect solution, I'm really just hoping to gather consensus among people who are running existing trove installations and have yet to upgrade to the newer code about what would be easiest for them.  My understanding is that list is basically HP and Rackspace, and maybe Ebay?, but the hope was that bringing the issue up on the list might confirm or refute that assumption and drive the conversation to a suitable workaround for those affected, which hopefully isn't that many organizations at this point.

The options are basically:

1. Put the onus on the deployer to correct existing records in the database.
2. Have the migration script put dummy data in the database which you have to correct.
3. Put the onus on the deployer to fill out values in the config value


On Dec 18, 2013, at 8:46 PM, Robert Myers <myer0052 at gmail.com<mailto:myer0052 at gmail.com>> wrote:

There is the database migration for datastores. We should add a function to  back fill the existing data with either a dummy data or set it to 'mysql' as that was the only possibility before data stores.

On Dec 18, 2013 3:23 PM, "Greg Hill" <greg.hill at rackspace.com<mailto:greg.hill at rackspace.com>> wrote:
I've been working on fixing a bug related to migrating existing installations to the new datastore code:


The basic gist is that existing instances won't have any data in the datastore_version_id field in the database unless we somehow populate that data during migration, and not having that data populated breaks a lot of things (including the ability to list instances or delete or resize old instances).  It's impossible to populate that data in an automatic, generic way, since it's highly vendor-dependent on what database and version they currently support, and there's not enough data in the older schema to populate the new tables automatically.

So far, we've come up with some non-optimal solutions:

1. The first iteration was to assume 'mysql' as the database manager on instances without a datastore set.
2. The next iteration was to make the default value be configurable in trove.conf, but default to 'mysql' if it wasn't set.
3. It was then proposed that we could just use the 'default_datastore' value from the config, which may or may not be set by the operator.

My problem with any of these approaches beyond the first is that requiring people to populate config values in order to successfully migrate to the newer code is really no different than requiring them to populate the new database tables with appropriate data and updating the existing instances with the appropriate values.  Either way, it's now highly dependent on people deploying the upgrade to know about this change and react accordingly.

Does anyone have a better solution that we aren't considering?  Is this even worth the effort given that trove has so few current deployments that we can just make sure everyone is populating the new tables as part of their upgrade path and not bother fixing the code to deal with the legacy data?


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