select entries.target
from
(
    select swh_directory_walk(revision.directory)
    from snapshot tablesample system (0.001)
    inner join snapshot_branches using snapshot_id
    inner join snapshot_branch using branch_id
    inner join revision on (snapshot_branch.target = revision.id
                           and snapshot_branch.target_type = 'revision')
) as entries
where entries.type = 'file';