Optimize AzureBlobStore#delete method

[dadoonet]

From @dadoonet on February 17, 2015 22:16

When we have to remove a lot of files, method AzureBlobStore#delete is called for each file and generates a Azure API call.

Would be nice to see if we can batch somehow those calls instead.

Copied from original issue: elastic/elasticsearch-cloud-azure#66

[dadoonet]

@imotov As far as I understand the core code, I don't really think that it's doable. We need to process file deletion one by one, right?

[dadoonet]

From @imotov on July 29, 2015 15:25

@dadoonet actually when we delete a lot of files, we have a list of blobs that should be deleted and we simply iterate through the list. We can easily modify the logic to pass entire list to the store.

[imotov]

The feature in core was implemented and merged #12587. Now we need to take advantage of it in the azure plugin.

[dadoonet]

I believe that we can close it as we merged #18813. We can revisit it if at some point we find some optimizations in Azure SDK.