The S3 client creates a separate HTTP connection pool per scheduling group. Previously, the pool size was hardcoded as shares/100, yielding 1-10 connections. This was not tunable and could under-provision connections for groups with low share counts.
**Changes**
- A missing include (short_streams.hh) in sstables_loader.cc is added first to fix CMake builds where the header is not transitively included.
- The hardcoded per-share divisor is replaced with a per-shard connection budget. The new `object_storage_connections_per_shard` config option (default 128) specifies the total number of connections available on each shard. Connections are distributed proportionally across scheduling groups based on their shares: `max_connections = budget * group_shares / total_shares`. Remainder connections are assigned to the group with the most shares. When a new scheduling group client is created, all existing groups are rebalanced via `set_maximum_connections`. Creation and rebalance are serialized with a semaphore to prevent concurrent rebalances from racing.
- The config option is made live-updateable: a `storage_manager` observer propagates changes to all existing S3 clients, triggering rebalance under the same semaphore.
Fixes: https://scylladb.atlassian.net/browse/SCYLLADB-1704
No backport needed since this change affects KS on object storage which is not operational yet.
Closesscylladb/scylladb#29719
* github.com:scylladb/scylladb:
s3: make connections_per_shard live-updateable
s3: distribute connection pool proportionally across scheduling groups
4b13b24695