ceph: make computed measures read async

With this change Gnocchi will fetch all measures associated with
a metric in parallel using the Ceph aio API.

Change-Id: Idcab0eb447962f0d3c049f301b543806b673c869

gnocchi/storage/ceph.py

@@ -17,6 +17,7 @@ from collections import defaultdict
 import contextlib
 import datetime
 import errno
+import functools
 import itertools
 import uuid
 
@@ -234,9 +235,35 @@ class CephStorage(_carbonara.CarbonaraBasedStorage):
         object_names = list(self._list_object_names_to_process(object_prefix))
 
         measures = []
-        for n in object_names:
-            data = self._get_object_content(n)
-            measures.extend(self._unserialize_measures(n, data))
+        ops = []
+        bufsize = 8192  # Same sa rados_read one
+
+        tmp_measures = {}
+
+        def add_to_measures(name, comp, data):
+            if name in tmp_measures:
+                tmp_measures[name] += data
+            else:
+                tmp_measures[name] = data
+            if len(data) < bufsize:
+                measures.extend(self._unserialize_measures(name,
+                                                           tmp_measures[name]))
+                del tmp_measures[name]
+            else:
+                ops.append(self.ioctx.aio_read(
+                    name, bufsize, len(tmp_measures[name]),
+                    functools.partial(add_to_measures, name)
+                ))
+
+        for name in object_names:
+            ops.append(self.ioctx.aio_read(
+                name, bufsize, 0,
+                functools.partial(add_to_measures, name)
+            ))
+
+        while ops:
+            op = ops.pop()
+            op.wait_for_complete_and_cb()
 
         yield measures
 

releasenotes/notes/ceph-read-async-ca2f7512c6842adb.yaml

@@ -0,0 +1,4 @@
+---
+other:
+  - ceph driver now uses the rados async api to retrieve
+    measurements to process in parallel.