Files
notifications-admin/app/notify_client/cache.py
Chris Hill-Scott 589dbea971 Make Redis hold onto cached API responses longer
Redis is giving us a big performance boost (it’s roughly halved the
median request time on the admin app).

Once we’re confident that it’s working properly[1] we can eke out a bit
more performance from it by keeping the caches alive for longer. As
far as I can tell we’re still using Redis in a very low-volume way[2],
so increasing the number of things we’re storing shouldn’t start taxing
our Redis server at all. But reducing the number of times we have to
hit the API to refresh the cache _should_ result in some performance
increase.

---

1. ie we’re not seeing instances of stale caches not being invalidated

2. We have 2.5G of available space in Redis. Here is our current usage:
```
used_memory:7728960
used_memory_human:7.37M
used_memory_rss:7728960
used_memory_peak:16563776
used_memory_peak_human:15.79M
used_memory_lua:37888
```
2018-04-23 17:07:41 +01:00

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import json
from contextlib import suppress
from datetime import timedelta
from functools import wraps
from inspect import signature
TTL = int(timedelta(days=7).total_seconds())
def _get_argument(argument_name, client_method, args, kwargs):
with suppress(KeyError):
return kwargs[argument_name]
with suppress(ValueError, IndexError):
argument_index = list(signature(client_method).parameters).index(argument_name)
return args[argument_index - 1] # -1 because `args` doesnt include `self`
with suppress(KeyError):
return signature(client_method).parameters[argument_name].default
raise TypeError("{}() takes no argument called '{}'".format(
client_method.__name__, argument_name
))
def _make_key(key_format, client_method, args, kwargs):
return key_format.format(**{
argument_name: _get_argument(argument_name, client_method, args, kwargs)
for argument_name in list(signature(client_method).parameters)
})
def set(key_format):
def _set(client_method):
@wraps(client_method)
def new_client_method(client_instance, *args, **kwargs):
redis_key = _make_key(key_format, client_method, args, kwargs)
cached = client_instance.redis_client.get(redis_key)
if cached:
return json.loads(cached.decode('utf-8'))
api_response = client_method(client_instance, *args, **kwargs)
client_instance.redis_client.set(
redis_key,
json.dumps(api_response),
ex=TTL,
)
return api_response
return new_client_method
return _set
def delete(key_format):
def _delete(client_method):
@wraps(client_method)
def new_client_method(client_instance, *args, **kwargs):
redis_key = _make_key(key_format, client_method, args, kwargs)
client_instance.redis_client.delete(redis_key)
return client_method(client_instance, *args, **kwargs)
return new_client_method
return _delete