Common Memcached use cases

Memcached is an application-controlled key-value cache: your code decides what to store, under which key, and for how long. That makes it a good fit for a handful of recurring patterns. This article walks through the most common ones and closes with a note on when Memcached is the right tool versus the proxy cache.

Updated 3 Aug 20263 min read

Session store

Storing user sessions and short-lived authentication state in Memcached keeps reads fast and takes that load off your database. Sessions are a natural fit: they are small, read on almost every request, and safe to lose — if a session disappears the user simply signs in again.

Set a TTL that matches your session lifetime so expiry is handled by the cache rather than by application cleanup. Remember that each region has its own cache, so if a user's requests can land in different regions, keep the session's source of truth somewhere shared, or pin the user to a region.

Query and computed-result cache

Caching the result of an expensive database query or a costly computation is the classic use of Memcached. Build a key from the query parameters, store the result with a TTL, and check the cache before doing the work again:

key   = "user:1234:dashboard"
value = <serialised result>
ttl   = 300 seconds

On a miss, run the query, store the result, and return it. On a hit, skip the work entirely. This pattern shines for read-heavy data that changes infrequently — reference tables, aggregate counts, rendered reports. Always handle the miss path, because an entry can expire or be evicted at any time.

Rate-limit and counter storage

Memcached's atomic increment makes it well suited to counters — request counts for rate limiting, view counts, feature-usage tallies. Increment a per-key counter with a short TTL and read it to decide whether a caller is over their limit:

key = "ratelimit:api:198.51.100.7:minute"
incr by 1, expire 60 seconds

Because counters are cheap and short-lived, this keeps rate-limit checks off your database. Note that each region counts independently; if you need a single global limit, that requires coordination beyond a per-region cache.

Fragment and page-fragment cache

If your application renders HTML or assembles responses from expensive pieces, cache the rendered fragments — a navigation menu, a product card, a sidebar — under stable keys and reuse them across requests. This is application-controlled, so you decide exactly which fragments are cacheable and can invalidate a fragment the moment its underlying data changes by deleting its key.

Memcached or the proxy cache?

Both reduce load, but they work at different layers:

Reach for Memcached when your application needs to control the cache — arbitrary keys, partial-page fragments, counters, session data, or anything keyed on something other than the request URL.
Reach for the proxy cache when you want to cache whole HTTP responses transparently in front of an HTTP container, with no application changes.

They are complementary — many applications use the proxy cache for public read endpoints and Memcached for per-user and computed data behind them. For a full decision guide, see Proxy cache vs Memcached.