Snapshot deletion and creation slow down as number of snapshots in repository grows

[imotov]

In order to create a new snapshot or delete an existing snapshot, elasticsearch has to load all existing shard level snapshots to figure out which files need to be copied and which files can be cleaned. The number of files to be checked is equal to number_of_shards * number_of_snapshots, which on a large clusters and frequent snapshots can lead to very long operation times especially with non-filesystem repositories. See elastic/elasticsearch-cloud-aws#150 and this group post for examples of issues that this behavior is causing.

[nickcanz]

Just wanted to chime in, this issue has affected us a great deal as well. It made "sense" after I thought it through, how ES snapshotting works, but was an unpleasant surprise.

[niemyjski]

I seem to be seeing this behavior with azure blob storage after upgrading to 1.7.5