# Caches: drivers and what they hold

Nothing is cached unless you add it. [Caches](caches.md) says how
you add a cache and how its copies stay current. This topic says which
services can hold a cache and what a cache may hold.

## Redis-compatible services

Upstash, Valkey, Amazon ElastiCache and Redis itself all use the Redis
driver, on the native target and on Workers. Each service's settings are
listed on the driver's page, as every driver's are
([Connecting in `app.jadpo`](connecting-in-app-jadpo.md)).

## `Driver.memory`

`Driver.memory` keeps a cache in each server's own memory. Each server
then has its own cache, emptied on every restart. You may use it in
production, and `jadpo check` warns you when you do. On Workers it is a
compile error, because a Worker keeps no memory between requests.

## Cloudflare KV

Cloudflare KV isn't a cache driver. A change to KV can take a minute to
reach every location, so an entry you invalidated could still be served.
An app that wants KV calls it as a package.

## What a cache may hold

A cache holds only what is harmless to lose: cached records and query
results, route rate limits, and provider rate limits shared across
servers. All of them go through the same `rate_limits: { store: cache }`
and caching settings.

A cache never holds idempotency keys, webhook de-duplication, sessions,
OAuth grants, poll state, schedule leases, batch positions, the records
of a multi-step call or the outbox. Each of those must survive a
restart, so each lives in a database. Naming a cache-only store for one
of them is a compile error naming the feature.