FAQs
This section gives information about some FAQs regarding Spanner migration tool.
Table of contents
How to start the Spanner Migration Tool UI ?
To bring up the Spanner Migration Tool UI, please follow the steps mentioned here.
Can Spanner Migration Tool be used without connecting to the spanner instance?
Yes, Spanner Migration Tool can be used for schema assessment and modifications without connecting to the spanner instance
When is a table interleavable?
A table is interleavable into a parent table if it has a foreign key referencing the parent table and the primary key is a superset of the primary key of the parent table.
What to do in case you are unable to connect to a spanner instance?
If you are connecting from a GCE VM please verify the access scope of your GCE VM. It should be set to Allow full access to all Cloud APIs to allow connections to Cloud API. In case it is set to default access, please modify the access level by following the steps below and try again -
- Stop the VM
- Edit the VM configuration and change the access scope to Allow full access to all Cloud APIs.
- Restart the VM
Otherwise, execute the following command: gcloud auth application-default login
What happens behind the scenes in minimal downtime migration?
Spanner Migration Tool orchestrates the entire process using a unified interface, which comprises the following steps:
- Setting up a GCS bucket to store incoming change events on the source database while the snapshot migration progresses.
- Setting up the bulk load of the snapshot data and stream of incoming change events using Datastream. Within the Spanner Migration Tool UI, source and target connection profile will need to be setup
- Setting up the Dataflow job to migrate the change events into Spanner, which drains the GCS bucket over time.
Once the GCS bucket is almost empty, users need to stop writing to the source database so that the remaining change events can be applied. This results in a short downtime while Spanner catches up to the source database. Afterwards,the application can be cut over to Spanner. Currently, Spanner Migration Tool provides minimal downtime migration support for MySQL, Oracle and PostgreSQL databases.