> ## Documentation Index
> Fetch the complete documentation index at: https://gcore-doc-1046.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Cache

Cache is a fast key-value store co-located with each FastEdge POP (Point of Presence). It is intended for transient, request-time state ( counters, memoized computations, idempotency tokens ) and is available to every FastEdge application on a paid plan at runtime without needing to be created or linked in advance.

## How it works

**POP-local scope**: Cache data lives inside a single POP. Writes are not replicated to other POPs, and a value written in one POP is not visible from another. Within a POP, reads and writes are strongly consistent.

**Transient storage**: Entries are evictable and carry no durability guarantee. Values may disappear before their expiration if the POP is under memory pressure. Cache is not a substitute for persistent storage.

**Atomic counters**: Integer counters can be incremented and decremented atomically within a POP. This makes Cache suitable for primitives such as rate limiting and fixed-window throttling.

**Coalesced population (JS only)**: A `getOrSet` operation prevents duplicate work within a single WASM instance — concurrent callers for the same key share one populator execution. This convenience is currently exposed by the JavaScript SDK only.

## When to use Cache vs Edge Storage

Cache and [Edge Storage](/fastedge/kv-stores/how-it-works) solve different problems. Use this table to decide which one fits your workload.

|                     | Cache                                                                          | Edge Storage (KV)                                                                   |
| ------------------- | ------------------------------------------------------------------------------ | ----------------------------------------------------------------------------------- |
| Scope               | Single POP                                                                     | Globally replicated to all POPs                                                     |
| Consistency         | Strong (within a POP)                                                          | Eventual (1–2 seconds globally)                                                     |
| Durability          | Transient, evictable                                                           | Durable, backed by a central database                                               |
| Provisioning        | None — available at runtime on paid plans                                      | Created in the Customer Portal and linked to your application                       |
| Writes from the API | No (runtime only)                                                              | Yes                                                                                 |
| Atomic counters     | Yes (`incr`; `decr` JS only)                                                   | No                                                                                  |
| Typical workloads   | Rate limits, response memoization, idempotency keys, per-request deduplication | Configuration, feature flags, lookup tables, blocklists, sorted sets, Bloom filters |

A common pattern is to use both together: store the source of truth in Edge Storage and use Cache to memoize derived results or to enforce per-POP rate limits.

## API surface

The Cache API is exposed to FastEdge applications via the SDK. The available operations are:

* **Reading and writing**: `get`, `set`, `delete`, `exists`
* **Atomic operations and TTL**: `incr`, `decr` (JS only), `expire`
* **Get-or-populate**: `getOrSet` (JS only) for read-through caching with coalesced population

Expiration is specified per write as a TTL (`ttl`, `ttlMs`) or an absolute deadline (`expiresAt`). Entries with no expiration remain until evicted.

## Accessing Cache in applications

For more information regarding Cache usage in applications, see the [JavaScript SDK](https://g-core.github.io/FastEdge-sdk-js/reference/fastedge/cache/) and the [Rust SDK](https://docs.rs/fastedge/latest/fastedge/cache/).

<Info>
  **Info**

  Cache does not need to be created or linked to your application. It is available to every FastEdge application on a paid plan at runtime by importing the cache module from the SDK.
</Info>