Indicates whether the index is currently backfilling. Backfilling is the process of reading items from the table and determining whether they can be added to the index. (Not all items will qualify: For example, a partition key cannot have any duplicate values.) If an item can be added to the index, DynamoDB will do so. After all items have been processed, the backfilling operation is complete and Backfilling is false.
For indexes that were created during a CreateTable operation, the Backfilling
attribute does not appear in the DescribeTable output.