Caching¶

Added in version 3.9.0.

coredis allows using a client side cache to eliminate readonly requests to the redis server when a response is available in the local cache.

If enabled the clients will cache the responses for readonly commands by key/command/arguments. The coredis clients accept any cache implementing the AbstractCache interface and will:

Cache responses for readonly commands acting on single keys (the docstring for the method will indicate whether it supports caching, for example get()).
Return cached responses when they are found if the cache is returning healthy via the healthy property
Invalidate the entire cache for a key if a non readonly command is called
If the cache implements SupportsSampling and returns a confidence value lower than 100 the client will distrust the cached response (100-$confidence)% of the time and validate the cached response against the actual response from the server. The result of the comparison will be provided to the cache through a call to feedback() and it is up to the cache implementation to decide what to do with this feedback.

Tracking Cache¶

coredis currently ships with an implementation of Server assisted client side caching that can be used with both the standalone Redis client or the RedisCluster client. This implementation enables client tracking for the client so that the redis server remembers which keys the client has requested and if the key is modified (whether mutated, deleted or expired) sends a notification that the cache subscribes to to invalidate the cache.

Specifically NodeTrackingCache contains the implementation for a single node and ClusterTrackingCache tracks all the nodes in a redis cluster.

For convenience a proxy class that automatically picks the right implementation based on the client is available as TrackingCache.

For example:

import asyncio
import coredis
from coredis.cache import TrackingCache

cached_client = coredis.Redis(cache=TrackingCache())
regular_client = coredis.Redis()

# or in cluster mode
# cached_client = coredis.RedisCluster("localhost", 7000, cache=InvalidatingCache())
# regular_client = coredis.RedisCluster("localhost", 7000)

async def test():
    assert not await cached_client.get("fubar") # None response cached
    await regular_client.set("fubar", "bar") # <- triggers a push message to cached_client
    await asyncio.sleep(0.01)
    assert b"bar" == await cached_client.get("fubar") # Cache should be invalidated
    assert b"bar" == await cached_client.get("fubar") # Fetched from local cache
    await cached_client.delete(["fubar"]) # Invalidates local cache immediately
    assert not await cached_client.get("fubar")

asyncio.run(test())

TrackingCache exposes a few configuration options to fine tune the cache. Specifically the following constructor arguments might be of interest:

max_size_bytes: Maximum size in bytes that the cache should be allowed to grow to. The cache will periodically shrink the cache in an LRU manner until it is below the threshold.
max_keys: Maximum number of redis keys to track. This does not map directly to the number of cached entries as the cache maintains a per key, per command, per argument cache.
max_idle_time_seconds: Maximum time to tolerate no repsonse from the server. The cache instance will use the PING command to verify if the server is responsive even if no invalidation notifications have been received and if the threshold is breached the in memory cache will be reset and the cache marked unhealthy.
confidence: Confidence % in the cache. The client will sample cached values based on the confidence and if the cached value is not the same as the actual response from the server the actual value will be returned and the tainted key invalidated.
dynamic_confidence: If set to True the cache will adjust it’s confidence based on sampled (sampling depends on the initial confidence value itself) validations.