TTLCache - an in-memory cache with item expiration
Features
- Simple API.
- Type parameters.
- Item expiration and automatic deletion.
- Automatic expiration time extension on each
Getcall. Loaderinterface that is used to load/lazily initialize missing cache items.- Subscription to cache events (insertion and eviction).
- Metrics.
- Configurability.
Installation
go get github.com/jellydator/ttlcache/v3
Usage
The main type of ttlcache is Cache. It represents a single
in-memory data store.
To create a new instance of ttlcache.Cache, the ttlcache.New() function
should be called:
func main() {
cache := ttlcache.New[string, string]()
}Note that by default, a new cache instance does not let any of its
items to expire or be automatically deleted. However, this feature
can be activated by passing a few additional options into the
ttlcache.New() function and calling the cache.Start() method:
func main() {
cache := ttlcache.New[string, string](
ttlcache.WithTTL[string, string](30 * time.Minute),
)
go cache.Start() // starts automatic expired item deletion
}Even though the cache.Start() method handles expired item deletion well,
there may be times when the system that uses ttlcache needs to determine
when to delete the expired items itself. For example, it may need to
delete them only when the resource load is at its lowest (e.g., after
midnight, when the number of users/HTTP requests drops). So, in situations
like these, instead of calling cache.Start(), the system could
periodically call cache.DeleteExpired():
func main() {
cache := ttlcache.New[string, string](
ttlcache.WithTTL[string, string](30 * time.Minute),
)
for {
time.Sleep(4 * time.Hour)
cache.DeleteExpired()
}
}The data stored in ttlcache.Cache can be retrieved and updated with
Set, Get, Delete, etc. methods:
func main() {
cache := ttlcache.New[string, string](
ttlcache.WithTTL[string, string](30 * time.Minute),
)
// insert data
cache.Set("first", "value1", ttlcache.DefaultTTL)
cache.Set("second", "value2", ttlcache.NoTTL)
cache.Set("third", "value3", ttlcache.DefaultTTL)
// retrieve data
item := cache.Get("first")
fmt.Println(item.Value(), item.ExpiresAt())
// delete data
cache.Delete("second")
cache.DeleteExpired()
cache.DeleteAll()
}To subscribe to insertion and eviction events, cache.OnInsertion() and
cache.OnEviction() methods should be used:
func main() {
cache := ttlcache.New[string, string](
ttlcache.WithTTL[string, string](30 * time.Minute),
ttlcache.WithCapacity[string, string](300),
)
cache.OnInsertion(func(item *ttlcache.Item[string, string]) {
fmt.Println(item.Value(), item.ExpiresAt())
})
cache.OnEviction(func(reason ttlcache.EvictionReason, item *ttlcache.Item[string, string]) {
if reason == ttlcache.EvictionReasonCapacityReached {
fmt.Println(item.Key(), item.Value())
}
})
cache.Set("first", "value1", ttlcache.DefaultTTL)
cache.DeleteAll()
}To load data when the cache does not have it, a custom or
existing implementation of ttlcache.Loader can be used:
func main() {
loader := ttlcache.LoaderFunc[string, string](
func(c *ttlcache.Cache[string, string], key string) *ttlcache.Item[string, string] {
// load from file/make an HTTP request
item := c.Set("key from file", "value from file")
return item
},
)
cache := ttlcache.New[string, string](
ttlcache.WithLoader[string, string](loader),
)
item := cache.Get("key from file")
}