Add support for limiting the number of samples returned

Blueprint: api-limit

Change-Id: Id053eb60674fea58b3d83b460fd0344dbc050cbf
Signed-off-by: Julien Danjou <julien@danjou.info>

ceilometer/storage/base.py

@@ -126,8 +126,11 @@ class Connection(object):
         """
 
     @abc.abstractmethod
-    def get_samples(self, sample_filter):
+    def get_samples(self, sample_filter, limit=None):
-        """Return an iterable of model.Sample instances
+        """Return an iterable of model.Sample instances.
+
+        :param sample_filter: Filter.
+        :param limit: Maximum number of results to return.
         """
 
     @abc.abstractmethod

ceilometer/storage/impl_hbase.py

@@ -393,8 +393,11 @@ class Connection(base.Connection):
                 user_id=data['f:user_id'],
             )
 
-    def get_samples(self, sample_filter):
+    def get_samples(self, sample_filter, limit=None):
-        """Return an iterable of models.Sample instances
+        """Return an iterable of models.Sample instances.
+
+        :param sample_filter: Filter.
+        :param limit: Maximum number of results to return.
         """
         def make_sample(data):
             """ transform HBase fields to Sample model
@@ -415,6 +418,9 @@ class Connection(base.Connection):
             # properly.
             # handle metaquery
             metaquery = sample_filter.metaquery
+            # TODO(jd) implements using HBase capabilities
+            if limit == 0:
+                break
             if len(metaquery) > 0:
                 # metaquery checks resource table
                 resource = self.resource.row(meter['f:resource_id'])
@@ -423,8 +429,12 @@ class Connection(base.Connection):
                     if resource['f:r_' + k.split('.', 1)[1]] != v:
                         break   # if one metaquery doesn't match, break
                 else:
+                    if limit:
+                        limit -= 1
                     yield make_sample(meter)
             else:
+                if limit:
+                    limit -= 1
                 yield make_sample(meter)
 
     def _update_meter_stats(self, stat, meter):

ceilometer/storage/impl_log.py

@@ -100,7 +100,7 @@ class Connection(base.Connection):
         return []
 
     def get_meters(self, user=None, project=None, resource=None, source=None,
-                   metaquery={}):
+                   limit=None, metaquery={}):
         """Return an iterable of dictionaries containing meter information.
 
         { 'name': name of the meter,
@@ -114,6 +114,7 @@ class Connection(base.Connection):
         :param project: Optional ID for project that owns the resource.
         :param resource: Optional resource filter.
         :param source: Optional source filter.
+        :param limit: Maximum number of results to return.
         :param metaquery: Optional dict with metadata to match on.
         """
         return []

ceilometer/storage/impl_mongodb.py

@@ -440,12 +440,16 @@ class Connection(base.Connection):
                     user_id=r['user_id'],
                 )
 
-    def get_samples(self, sample_filter):
+    def get_samples(self, sample_filter, limit=None):
-        """Return an iterable of samples as created by
+        """Return an iterable of model.Sample instances.
-        :func:`ceilometer.meter.meter_message_from_counter`.
+
+        :param sample_filter: Filter.
+        :param limit: Maximum number of results to return.
         """
+        if limit == 0:
+            return
         q = make_query_from_filter(sample_filter, require_meter=False)
-        samples = self.db.meter.find(q)
+        samples = self.db.meter.find(q).limit(limit or 0)
         for s in samples:
             # Remove the ObjectId generated by the database when
             # the sample was inserted. It is an implementation

ceilometer/storage/impl_sqlalchemy.py

@@ -311,12 +311,20 @@ class Connection(base.Connection):
                     user_id=resource.user_id,
                 )
 
-    def get_samples(self, sample_filter):
+    def get_samples(self, sample_filter, limit=None):
-        """Return an iterable of api_models.Samples
+        """Return an iterable of api_models.Samples.
+
+        :param sample_filter: Filter.
+        :param limit: Maximum number of results to return.
         """
+        if limit == 0:
+            return
+
         query = self.session.query(Meter)
         query = make_query_from_filter(query, sample_filter,
                                        require_meter=False)
+        if limit:
+            query = query.limit(limit)
         samples = query.all()
 
         for s in samples:

tests/storage/base.py

@@ -271,6 +271,16 @@ class MeterTest(DBTestBase):
 
 class RawSampleTest(DBTestBase):
 
+    def test_get_samples_limit_zero(self):
+        f = storage.SampleFilter()
+        results = list(self.conn.get_samples(f, limit=0))
+        self.assertEqual(len(results), 0)
+
+    def test_get_samples_limit(self):
+        f = storage.SampleFilter()
+        results = list(self.conn.get_samples(f, limit=3))
+        self.assertEqual(len(results), 3)
+
     def test_get_samples_by_user(self):
         f = storage.SampleFilter(user='user-id')
         results = list(self.conn.get_samples(f))
@@ -278,6 +288,16 @@ class RawSampleTest(DBTestBase):
         for meter in results:
             assert meter.as_dict() in [self.msg1, self.msg2]
 
+    def test_get_samples_by_user_limit(self):
+        f = storage.SampleFilter(user='user-id')
+        results = list(self.conn.get_samples(f, limit=1))
+        self.assertEqual(len(results), 1)
+
+    def test_get_samples_by_user_limit_bigger(self):
+        f = storage.SampleFilter(user='user-id')
+        results = list(self.conn.get_samples(f, limit=42))
+        self.assertEqual(len(results), 2)
+
     def test_get_samples_by_project(self):
         f = storage.SampleFilter(project='project-id')
         results = list(self.conn.get_samples(f))