[openstack-dev] Online Migrations.
philip.schwartz at RACKSPACE.COM
Wed Jun 10 20:16:54 UTC 2015
I am taking over work on https://review.openstack.org/#/c/154521/ from Johanness and have spent some time today discussing the current patchset and what is remaining with Dan and Johannes.
I wanted to broach the topic of the remaining development with the lists to make sure we go in the right direction with it as it is not an easy problem to solve.
The remaining work is to have a way of preventing database contracts from running until data migrations that the column interacts with are complete, this is not an easy problem to solve as the goal of the online migrations is to do pure model based schema migrations and there is no way of currently identifying when a data migration has taken place and a contract is safe to perform.
The first thought I had was to default to a requirement of a data migration removing data from a column and have the default check of the contract be one of verifying that the column is currently empty. This has the issue of not working in all cases, especially around Foreign Keys.
At this point I would like to open this discussion up to all in order to make sure the best solution is chosen for this problem..
More information about the OpenStack-dev