Support multiple batch columns for batched background migrations
The current batched background migration framework makes the assumption that a table will only be batched over a single column. Even in the default strategy that uses on primary key batching, this is a poor assumption to make, as some tables have multi-column primary keys.
Now that the migration framework has proven itself, we should expand to support multiple batch columns to better support other use cases.
One hurdle here is that the PrimaryKeyBatchingStrategy
depends on EachBatch
, which only supports a single column.