record last_collected timestamp for tenants

Otherwise, we keep rescanning empty hours every run,
which is stupid.

Change-Id: Ifb52065edb600e4b8bb157b5fab083a17af63e60

artifice/api/web.py

@@ -79,10 +79,9 @@ def collect_usage(tenant, db, session, resp, end):
     timestamp = datetime.now()
     session.begin(subtransactions=True)
     print 'collect_usage for %s %s' % (tenant.id, tenant.name)
-    db.insert_tenant(tenant.id, tenant.name,
+    db_tenant = db.insert_tenant(tenant.id, tenant.name,
                     tenant.description, timestamp)
-    start = session.query(func.max(UsageEntry.end).label('end')).\
-        filter(UsageEntry.tenant_id == tenant.id).first().end
+    start = db_tenant.last_collected
     if not start:
         print 'failed to find any previous usageentry for this tenant; starting at %s' % dawn_of_time
         start = dawn_of_time
@@ -112,6 +111,10 @@ def collect_usage(tenant, db, session, resp, end):
                     db.insert_usage(tenant.id, res, transformed,
                         window_start, window_end, timestamp)
 
+            # update the timestamp for the tenant so we won't examine this timespan again.
+            db_tenant.last_collected = window_end
+            session.add(db_tenant)
+
             session.commit()
             resp["tenants"].append(
                 {"id": tenant.id,

artifice/database.py

@@ -17,12 +17,16 @@ class Database(object):
         query = self.session.query(Tenant).\
             filter(Tenant.id == tenant_id)
         if query.count() == 0:
-            self.session.add(Tenant(id=tenant_id,
-                                    info=metadata,
-                                    name=tenant_name,
-                                    created=timestamp
-                                    ))
+            tenant = Tenant(id=tenant_id,
+                            info=metadata,
+                            name=tenant_name,
+                            created=timestamp
+                            )
+            self.session.add(tenant)
             self.session.flush()            # can't assume deferred constraints.
+            return tenant
+        else:
+            return query[0]
 
     def insert_resource(self, tenant_id, resource_id, resource_type, timestamp):
         query = self.session.query(Resource).\

artifice/models/__init__.py

@@ -81,6 +81,7 @@ class Tenant(Base):
     name = Column(Text, nullable=False)
     info = Column(Text)
     created = Column(DateTime, nullable=False)
+    last_collected = Column(DateTime, nullable=True)
 
     resources = relationship(Resource, backref="tenant")