What are blob keys and blob container in elasticsearch?

Elastic Stack Elasticsearch
1

What are blob keys and blob container in elasticsearch?

if (blobKeys.isEmpty() == false) {
                logger.warn("Could not find a readable index-N file in a non-empty shard snapshot directory [{}]"; blobContainer.path());
            }

What does the above piece of code mean ?

2

Where did that code come from?

3
4

Right, so it's talking about snapshots and the blob data that the repositories - s3 etc - are using.