Add caching logic to most expensive APIs

We've recently encountered a pretty major degradation in s3 API
performance. I originally skipped caching logic because things were
"good enough" and I was scared to mess up cache logic. However, page
loads are now routinely taking over 4s. My stats for the last 2 hours
were:

 Average: 1.876110 (0.649776 %stddev)

So the average isn't great and the standard deviation is huge which
means we get really common *large* outliers. This patch is built on 2
simple ideas:

 #1 - caching is safe for releases.l.o. This is safe because we publish
      here once a month and then things are "static".
 #2 - find_artifact and dir_list are the most expensive calls

for #1, we'll have to patch releases_us_secrets.py with:
    CACHES = {
        'default': {
            'BACKEND':
    django.core.cache.backends.filebased.FileBasedCache',
            'LOCATION': '/tmp/releases-django-cache',
            'TIMEOUT': 5 * 60,  # 5 minute cache
        }
    }

Change-Id: I3effd75a5946d6f8a95dc6a626436a02987f4617
Reviewed-on: https://review.linaro.org/12768
Reviewed-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Reviewed-by: Ben Copeland <ben.copeland@linaro.org>

4 files changed, 21 insertions, 3 deletions

diff --git a/license_protected_downloads/common.py b/license_protected_downloads/common.py
index e4755fd..0fe948a 100644
--- a/license_protected_downloads/common.py
+++ b/license_protected_downloads/common.py
@@ -4,6 +4,7 @@ import os
 import boto
 
 from django.conf import settings
+from django.core.cache import cache
 from django.http import Http404
 
 from license_protected_downloads import models
@@ -31,6 +32,16 @@ def safe_path_join(base_path, *paths):
     return target_path
 
 
+def cached_call(key, func, *args, **kwargs):
+    key = func.__name__ + key
+    v = cache.get(key)
+    if v:
+        return v
+    v = func(*args, **kwargs)
+    cache.set(key, v)
+    return v
+
+
 def _handle_wildcard(request, fullpath):
     path, name = os.path.split(fullpath)
 
diff --git a/license_protected_downloads/tests/__init__.py b/license_protected_downloads/tests/__init__.py
index 307b75f..805675e 100644
--- a/license_protected_downloads/tests/__init__.py
+++ b/license_protected_downloads/tests/__init__.py
@@ -1,4 +1,3 @@
-
 from license_protected_downloads.tests.test_buildinfo import *
 from license_protected_downloads.tests.test_api_v1 import *
 from license_protected_downloads.tests.test_api_v2 import *
diff --git a/license_protected_downloads/views.py b/license_protected_downloads/views.py
index 9ee198c..a1c670b 100644
--- a/license_protected_downloads/views.py
+++ b/license_protected_downloads/views.py
@@ -25,6 +25,7 @@ from group_auth_common import GroupAuthError
 import xml.dom.minidom as dom
 
 from license_protected_downloads.common import (
+    cached_call,
     dir_list,
     find_artifact,
 )
@@ -219,7 +220,7 @@ def _check_file_permission(request, artifact, internal):
 
 
 def file_server_get(request, path):
-    artifact = find_artifact(request, path)
+    artifact = cached_call(path, find_artifact, request, path)
     internal = get_client_ip(request) in config.INTERNAL_HOSTS
 
     if not internal:
@@ -233,7 +234,7 @@ def file_server_get(request, path):
                 return resp
 
     if artifact.isdir():
-        return _handle_dir_list(request, artifact)
+        return cached_call(path, _handle_dir_list, request, artifact)
 
     # prevent download of files like BUILD-INFO.txt
     if artifact.hidden():
diff --git a/settings.py b/settings.py
index 02c5244..ac74584 100644
--- a/settings.py
+++ b/settings.py
@@ -185,6 +185,13 @@ LOGGING = {
     }
 }
 
+# disable caches by default for testing (enabled in production)
+CACHES = {
+    'default': {
+        'BACKEND': 'django.core.cache.backends.dummy.DummyCache',
+    }
+}
+
 import django
 if django.VERSION < (1, 6):
     # old django needs a hack to not send emails for ALLOWED_HOSTS violations