diff --git a/swh/indexer/tasks.py b/swh/indexer/tasks.py
index 5ab5e15..92bf3ca 100644
--- a/swh/indexer/tasks.py
+++ b/swh/indexer/tasks.py
@@ -1,100 +1,110 @@
 # Copyright (C) 2016-2018  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import logging
 
 from swh.scheduler.task import Task as SchedulerTask
 
 from .mimetype import ContentMimetypeIndexer, MimetypeRangeIndexer
 from .language import ContentLanguageIndexer
 from .ctags import CtagsIndexer
 from .fossology_license import ContentFossologyLicenseIndexer
 from .rehash import RecomputeChecksums
 from .metadata import RevisionMetadataIndexer, OriginMetadataIndexer
 from .origin_head import OriginHeadIndexer
 
 logging.basicConfig(level=logging.INFO)
 
 
 class Task(SchedulerTask):
+    """Task whose results is needed for other computations.
+
+    """
     def run_task(self, *args, **kwargs):
         indexer = self.Indexer().run(*args, **kwargs)
         if hasattr(indexer, 'results'):  # indexer tasks
             return indexer.results
         return indexer
 
 
+class StatusTask(SchedulerTask):
+    """Task which returns a status either eventful or uneventful.
+
+    """
+    def run_task(self, *args, **kwargs):
+        results = self.Indexer().run(*args, **kwargs)
+        return {'status': 'eventful' if results else 'uneventful'}
+
+
 class RevisionMetadata(Task):
     task_queue = 'swh_indexer_revision_metadata'
 
     serializer = 'msgpack'
 
     Indexer = RevisionMetadataIndexer
 
 
 class OriginMetadata(Task):
     task_queue = 'swh_indexer_origin_intrinsic_metadata'
 
     Indexer = OriginMetadataIndexer
 
 
 class OriginHead(Task):
     task_queue = 'swh_indexer_origin_head'
 
     Indexer = OriginHeadIndexer
 
 
-class ContentMimetype(Task):
-    """Task which computes the mimetype, encoding from the sha1's content.
+class ContentMimetype(StatusTask):
+    """Compute (mimetype, encoding) from the sha1's content.
 
     """
     task_queue = 'swh_indexer_content_mimetype'
-
     Indexer = ContentMimetypeIndexer
 
 
-class ContentRangeMimetype(Task):
-    """Compute mimetype, encoding on a range of sha1s.
+class ContentRangeMimetype(StatusTask):
+    """Compute (mimetype, encoding) on a range of sha1s.
 
     """
     task_queue = 'swh_indexer_content_mimetype_range'
-
     Indexer = MimetypeRangeIndexer
 
 
 class ContentLanguage(Task):
     """Task which computes the language from the sha1's content.
 
     """
     task_queue = 'swh_indexer_content_language'
 
     Indexer = ContentLanguageIndexer
 
 
 class Ctags(Task):
     """Task which computes ctags from the sha1's content.
 
     """
     task_queue = 'swh_indexer_content_ctags'
 
     Indexer = CtagsIndexer
 
 
 class ContentFossologyLicense(Task):
     """Task which computes licenses from the sha1's content.
 
     """
     task_queue = 'swh_indexer_content_fossology_license'
 
     Indexer = ContentFossologyLicenseIndexer
 
 
 class RecomputeChecksums(Task):
     """Task which recomputes hashes and possibly new ones.
 
     """
     task_queue = 'swh_indexer_content_rehash'
 
     Indexer = RecomputeChecksums