Way to cache your data

Embedded cache
Client server
Distributed cache
Revers proxy

Embedded cache

Java ConcurrentHashMap is not the best way to cache data. It is not complete main targets. Remember that Spring Cache use this implementation by default.
Guava / Caffeine / Ehcache is good choice when your application deployed in single instance mod (no shared state). It is contains main cache features like:
- automatic loading of entries into the cache, optionally asynchronously
- size-based eviction when a maximum is exceeded based on frequency and recency
- time-based expiration of entries, measured since last access or last write
- asynchronously refresh when the first stale request for an entry occurs
- keys automatically wrapped in weak references
- values automatically wrapped in weak or soft references
- notification of evicted (or otherwise removed) entries
- writes propagated to an external resource
- accumulation of cache access statistics
```
LoadingCache<Key, Graph> graphs = CacheBuilder.newBuilder()
    .maximumSize(1000)
    .expireAfterWrite(10, TimeUnit.MINUTES)
    .removalListener(MY_LISTENER)
    .build(new CacheLoader<Key, Graph>() {
        @Override
        public Graph load(Key key) throws AnyException {
            return createExpensiveGraph(key);
        }
    });
```

Client server cache

Memcached is simple key/value cache. Memcached's APIs provide a very large hash table distributed across multiple machines. When the table is full, subsequent inserts cause older data to be purged in least recently used (LRU) order.
- SpyMemcached
Redis is caching platform with transaction and lua scripting support. Main disadvantage is single worker thread.
- Redisson
- Jedis
- Ehcache
Ehcache can be started in distributed mod.
- Ehcache
Cloud cache provider (like Amazon ElastiCache)

Distributed cache

Hazelcast / Ignite / Tarantool. A distributed cache is a system that pools together the random-access memory (RAM) of multiple networked computers into a single in-memory data store used as a data cache to provide fast access to data.

Revers proxy cache

nginx / HAProxy / envoyproxy / Souin for Traefik - allows caching http traffic without understanding of incoming data. It can be useful when data is media, or it is a simple high frequency get queries without session.
```
# nginx example
http {
    # ...
    proxy_cache_path /data/nginx/cache keys_zone=one:10m;
    server {
        proxy_cache mycache;
        location / {
            proxy_pass http://localhost:8000;
        }
    }
}
```

Cache as a Sidecar / Ambassador

We can move cache close to application. We can move cache server to closer to application, in terms of Kubernetes we can deploy cache and application in same pod.

spec:
  containers:
    - name: app
      image: "app-image:latest"
    - name: cache
      image: "cache:latest"

Java Cache Guide

How we can cache data in Java applications

Nov 7, 2021 | - views

Problems

Way to cache your data

Embedded cache

Client server cache

Distributed cache

Revers proxy cache

Cache as a Sidecar / Ambassador