We had a maitenance downtime of our MySQL RDBMS, which is used as a Dremio source.
A lot of queries are using reflections on this source, and I was expecting that Dremio would use the reflections when Dremio source is offline, as if Dremio was online.
Instead of using reflection, Dremio does not execute the query and indicates the following message:
The source [CMS] is currently unavailable. Info: []
Is it the expected behaviour ? We are currently running Dremio CE 4.9.0.
Yes that is expected behavior, even if the query is reflected, Dremio requires the source to be available. The reason is the planner compares costs of SQL plans when going back to the dataset versus using reflection
In my opinion it is a bit surprising, as if I want that my Analytics be highly available, I need to materialize and create copies of data reflections contents (could use CTAS on S3 for example) , which I thought was the purpose of Dremio to avoid that (ie not having to create copies).