Removes the `_generic` postfix from the `GenericRemoteStorage` using
APIs, as `remote_storage` is the "default" now, and add a `_s3` postfix
to the remaining APIs using the S3 SDK (only in tenant snapshot). Also,
remove two unused functions: `list_objects_with_retries` and
`stream_tenants functions`.
Part of https://github.com/neondatabase/neon/issues/7547
Add two new functions `stream_objects_with_retries` and
`stream_tenants_generic` and use them in the `find-large-objects`
subcommand, migrating it to `remote_storage`.
Also adds the `size` field to the `ListingObject` struct.
Part of #7547
The find-large-objects scrubber subcommand is quite fast if you run it
in an environment with low latency to the S3 bucket (say an EC2 instance
in the same region). However, the higher the latency gets, the slower
the command becomes. Therefore, add a concurrency param and make it
parallelized. This doesn't change that general relationship, but at
least lets us do multiple requests in parallel and therefore hopefully
faster.
Running with concurrency of 64 (default):
```
2024-07-05T17:30:22.882959Z INFO lazy_load_identity [...]
[...]
2024-07-05T17:30:28.289853Z INFO Scanned 500 shards. [...]
```
With concurrency of 1, simulating state before this PR:
```
2024-07-05T17:31:43.375153Z INFO lazy_load_identity [...]
[...]
2024-07-05T17:33:51.987092Z INFO Scanned 500 shards. [...]
```
In other words, to list 500 shards, speed is increased from 2:08 minutes
to 6 seconds.
Follow-up of #8257, part of #5431
Adds a find-large-objects subcommand to the scrubber to allow listing
layer objects larger than a specific size.
To be used like:
```
AWS_PROFILE=dev REGION=us-east-2 BUCKET=neon-dev-storage-us-east-2 cargo run -p storage_scrubber -- find-large-objects --min-size 250000000 --ignore-deltas
```
Part of #5431
