Taught import to throttle at 25% of available workers.

When we expose  IMPORT_WORKERS_PERCENT, this becomes a configurable percentage.

fixes pulp#4068.

CHANGES/4068.bugfix

@@ -0,0 +1 @@
+Taught pulp-import to never use more than 25% of available worker-threads.

pulpcore/app/tasks/importer.py

@@ -8,6 +8,7 @@
 from gettext import gettext as _
 from logging import getLogger
 
+from django.conf import settings
 from django.core.files.storage import default_storage
 from django.db.models import F
 from naya.json import stream_array, tokenize
@@ -35,6 +36,7 @@
     RepositoryResource,
 )
 from pulpcore.constants import TASK_STATES
+from pulpcore.tasking.pulpcore_worker import Worker
 from pulpcore.tasking.tasks import dispatch
 
 from pulpcore.plugin.importexport import BaseContentResource
@@ -506,6 +508,15 @@ def safe_extract(tar, path=".", members=None, *, numeric_owner=False):
                             default_storage.save(base_path, f)
 
         # Now import repositories, in parallel.
+
+        # We want to limit the number of available-workers that import will consume, so that
+        # pulp can continue to work while doing an import. We accomplish this by creating a
+        # reserved-resource string for each repo-import-task based on that repo's index in
+        # the dispatch loop, mod number-of-workers-to-consume.
+        import_workers_percent = int(settings.get("IMPORT_WORKERS_PERCENT", 25))
+        total_workers = Worker.objects.online_workers().count()
+        import_workers = max(1, int(total_workers * (import_workers_percent / 100.0)))
+
         with open(os.path.join(temp_dir, REPO_FILE), "r") as repo_data_file:
             data = json.load(repo_data_file)
             gpr = GroupProgressReport(
@@ -517,14 +528,16 @@ def safe_extract(tar, path=".", members=None, *, numeric_owner=False):
             )
             gpr.save()
 
-            for src_repo in data:
+            for index, src_repo in enumerate(data):
+                # Lock the repo we're importing-into
                 dest_repo_name = _get_destination_repo_name(importer, src_repo["name"])
-
+                # pulpcore-worker limiter
+                worker_rsrc = f"import-worker-{index % import_workers}"
                 try:
                     dest_repo = Repository.objects.get(name=dest_repo_name)
                 except Repository.DoesNotExist:
                     if create_repositories:
-                        exclusive_resources = []
+                        exclusive_resources = [worker_rsrc]
                         dest_repo_pk = ""
                     else:
                         log.warning(
@@ -534,7 +547,7 @@ def safe_extract(tar, path=".", members=None, *, numeric_owner=False):
                         )
                         continue
                 else:
-                    exclusive_resources = [dest_repo]
+                    exclusive_resources = [dest_repo, worker_rsrc]
                     dest_repo_pk = dest_repo.pk
 
                 dispatch(