diff --git a/dashed/models.py b/dashed/models.py
index 03a9e186299..0505402864f 100644
--- a/dashed/models.py
+++ b/dashed/models.py
@@ -864,8 +864,12 @@ class DruidDatasource(Model, AuditMixinNullable, Queryable):
             return
         max_time = results[0]['result']['maxTime']
         max_time = parse(max_time)
-        intervals = (max_time - timedelta(seconds=1)).isoformat() + '/'
-        intervals += (max_time + timedelta(seconds=1)).isoformat()
+        # Query segmentMetadata for 7 days back. However, due to a bug,
+        # we need to set this interval to more than 1 day ago to exclude
+        # realtime segments, which trigged a bug (fixed in druid 0.8.2).
+        # https://groups.google.com/forum/#!topic/druid-user/gVCqqspHqOQ
+        intervals = (max_time - timedelta(days=7)).isoformat() + '/'
+        intervals += (max_time - timedelta(days=1)).isoformat()
         segment_metadata = client.segment_metadata(
             datasource=self.datasource_name,
             intervals=intervals)
@@ -1117,7 +1121,9 @@ class DruidMetric(Model, AuditMixinNullable):
     datasource_name = Column(
         String(250),
         ForeignKey('datasources.datasource_name'))
-    datasource = relationship('DruidDatasource', backref='metrics')
+    # Setting enable_typechecks=False disables polymorphic inheritance.
+    datasource = relationship('DruidDatasource', backref='metrics',
+                              enable_typechecks=False)
     json = Column(Text)
     description = Column(Text)
 
@@ -1139,7 +1145,9 @@ class DruidColumn(Model, AuditMixinNullable):
     datasource_name = Column(
         String(250),
         ForeignKey('datasources.datasource_name'))
-    datasource = relationship('DruidDatasource', backref='columns')
+    # Setting enable_typechecks=False disables polymorphic inheritance.
+    datasource = relationship('DruidDatasource', backref='columns',
+                              enable_typechecks=False)
     column_name = Column(String(256))
     is_active = Column(Boolean, default=True)
     type = Column(String(32))