publishRenameConcurrency (publish_rename_concurrency in YAML) sets how
many index files RenameFiles renames at once. It defaults to 4, the
value that was hard-coded, and 1 renames them one at a time. Values
below 1 are treated as 1, since a semaphore with no capacity would
never admit a rename.
The setting is global rather than per publishing endpoint because the
renames run against every storage backend, not only S3.
Martin Simon
b80f151b6d