"
max_concurrent_for_each was added to seastar for replacing
sstable_directory::parallel_for_each_restricted by using
more efficient concurrency control that doesn't create
unlimited number of continuations.
The series replaces the use of sstable_directory::parallel_for_each_restricted
with max_concurrent_for_each and exposes the sstable_directory::do_for_each_sstable
via a static method.
This method is used here by table::snapshot to limit concurrency
do snapshot operations that suffer from the same unbound
concurrency problem sstable_directory solved.
In addition sstable_directory::_load_semaphore that was used
across calls to do_for_each_sstable was replaced by a static per-shard
semaphore that caps concurrency across all calls to `do_for_each_sstable`
on that shard. This makes sense since the disk is a shared resource.
In the future, we may want to have a load semaphore per device rather than
a single global one. We should experiment with that.
Test: unit(dev)
"
* tag 'max_concurrent_for_each-v5' of github.com:bhalevy/scylla:
table: snapshot: use max_concurrent_for_each
sstable_directory: use a external load_semaphore
test: sstable_directory_test: extract sstable_directory creation into with_sstable_directory
distributed_loader: process_upload_dir: use initial_sstable_loading_concurrency
sstables: sstable_directory: use max_concurrent_for_each
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