Add a detailed debug message in case of segment allocation fail

Added an extra detailed message in case of error in the partial segment
allocation fail. This message should not be present in production. This
message should help in the debugging of the related bug.

Related-Bug: #2086602
Change-Id: I49b6e5f3be86c19e0a9e657ee6fe5f61c3b81bb3

neutron/objects/plugins/ml2/base.py

@@ -55,6 +55,15 @@ class SegmentAllocation(metaclass=abc.ABCMeta):
                 query = query.order_by(rand_func())
             return query.first()
 
+    @classmethod
+    def get_all_unallocated_segments(cls, context, **filters):
+        with cls.db_context_reader(context):
+            columns = set(dict(cls.db_model.__table__.columns))
+            model_filters = {k: filters[k]
+                             for k in columns & set(filters.keys())}
+            return context.session.query(cls.db_model).filter_by(
+                allocated=False, **model_filters).all()
+
     @classmethod
     def allocate(cls, context, **segment):
         with cls.db_context_writer(context):

neutron/plugins/ml2/drivers/helpers.py

@@ -156,6 +156,22 @@ class SegmentTypeDriver(BaseTypeDriver):
             raise db_exc.RetryRequest(
                 exceptions.NoNetworkFoundInMaximumAllowedAttempts())
 
+        # NOTE(ralonsoh): this debug message is added to debug LP#2086602.
+        # Once fixed, it won't be needed. This debug message should not be
+        # released.
+        LOG.debug('Partial segment allocation fail:')
+        LOG.debug('  - Filters: %s', filters)
+        LOG.debug('  - Non allocated segments:')
+        for non_allocated_segment in (
+                self.segmentation_obj.get_all_unallocated_segments(context,
+                    **filters)):
+            LOG.debug('    - %s', non_allocated_segment)
+        if directory.get_plugin(plugin_constants.NETWORK_SEGMENT_RANGE):
+            LOG.debug('  - Network segment ranges:')
+            for srange in ns_range.NetworkSegmentRange.get_objects(
+                    context.elevated()):
+                LOG.debug('    - %s', srange)
+
     @db_api.retry_db_errors
     def _delete_expired_default_network_segment_ranges(self):
         ctx = context.get_admin_context()