config_service: optimize projects.get_metadata

appengine/config_service/projects.py

 # Copyright 2015 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 """Provides info about projects (service tenants)."""
 
 import logging
 
+from google.appengine.api import memcache
 from google.appengine.ext import ndb
 from google.appengine.ext.ndb import msgprop
 from protorpc import messages
 
 from components.config.proto import project_config_pb2
 from components.config.proto import service_config_pb2
 
 import common
 import storage
 
@@ skipping 70 matching lines @@
   }
 
 
 def get_metadata(project_ids):
   """Returns a mapping {project_id: metadata}.
 
   If a project does not exist, the metadata is None.
 
   The project metadata stored in project.cfg files in each project.
   """
-  return _get_project_configs(
-      project_ids, common.PROJECT_METADATA_FILENAME,
-      project_config_pb2.ProjectCfg)
+  cache_ns = 'projects.get_metadata'
+  cache_map = memcache.get_multi(project_ids, namespace=cache_ns)
+  result = {}
+  missing = []
+  for pid in project_ids:
+    if pid in cache_map:
+      # cache hit
+      binary = cache_map[pid]
+      if binary is None:
+        # project does not exist
+        result[pid] = None
+      else:
+        cfg = project_config_pb2.ProjectCfg()
+        cfg.ParseFromString(binary)
+        result[pid] = cfg
+    else:
+      # cache miss
+      missing.append(pid)
+
+  if missing:
+    fetched = _get_project_configs(
+        missing, common.PROJECT_METADATA_FILENAME,
+        project_config_pb2.ProjectCfg)
+    result.update(fetched)  # at this point result must have all project ids
+    # Cache metadata for 10 min. In practice, it never changes.
+    cache_map = {
+      pid: cfg.SerializeToString() if cfg else None
+      for pid, cfg in fetched.iteritems()
+    }
+    memcache.set_multi(cache_map, namespace=cache_ns, time=60 * 10)
+
+  return result
 
 
 def get_refs(project_ids):
   """Returns a mapping {project_id: list of refs}
 
   The ref list is None if a project does not exist.
 
   The list of refs stored in refs.cfg of a project.
   """
   cfgs = _get_project_configs(
@@ skipping 27 matching lines @@
   # TODO(nodir): optimize
   assert isinstance(project_ids, list)
   if not project_ids:
     return project_ids
   assert all(pid for pid in project_ids)
   all_project_ids = set(p.id for p in get_projects())
   return [
     pid for pid in project_ids
     if pid in all_project_ids
   ]