Documentation
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Overview ¶
Package cache provides general-purpose in-memory caches. Different caches provide different eviction policies suitable for specific use cases.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
This section is empty.
Types ¶
type Cache ¶
type Cache interface {
// Set inserts an entry in the cache. This will replace any entry with
// the same key that is already in the cache. The entry may be automatically
// expunged from the cache at some point, depending on the eviction policies
// of the cache and the options specified when the cache was created.
Set(key interface{}, value interface{})
// Get retrieves the value associated with the supplied key if the key
// is present in the cache.
Get(key interface{}) (value interface{}, ok bool)
// Remove synchronously deletes the given key from the cache. This has no effect if the key is not
// currently in the cache.
Remove(key interface{})
// RemoveAll synchronously deletes all entries from the cache.
RemoveAll()
// Stats returns information about the efficiency of the cache.
Stats() Stats
}
Cache defines the standard behavior of in-memory thread-safe caches.
Different caches can have different eviction policies which determine when and how entries are automatically removed from the cache.
Using a cache is very simple:
c := NewLRU(5*time.Second, // default per-entry ttl
5*time.Second, // eviction interval
500) // max # of entries tracked
c.Set("foo", "bar") // add an entry
value, ok := c.Get("foo") // try to retrieve the entry
if ok {
fmt.Printf("Got value %v\n", value)
} else {
fmt.Printf("Value was not found, must have been evicted")
}
type EvictionCallback ¶
type EvictionCallback func(key, value interface{})
EvictionCallback is a function that will be called on entry eviction from an ExpiringCache.
This callback will be invoked immediately after the entry is deleted from the `sync.Map` that backs this cache (using `Map.Delete()`). No locks are held during the invocation of this callback. The callback should not result in blocking calls to long-running operations, however.
type ExpiringCache ¶
type ExpiringCache interface {
Cache
// SetWithExpiration inserts an entry in the cache with a requested expiration time.
// This will replace any entry with the same key that is already in the cache.
// The entry will be automatically expunged from the cache at or slightly after the
// requested expiration time.
SetWithExpiration(key interface{}, value interface{}, expiration time.Duration)
// EvictExpired() synchronously evicts all expired entries from the cache
EvictExpired()
}
ExpiringCache is a cache with entries that are evicted over time
func NewLRU ¶
func NewLRU(defaultExpiration time.Duration, evictionInterval time.Duration, maxEntries int32) ExpiringCache
NewLRU creates a new cache with an LRU and time-based eviction model.
Cache eviction is done on a periodic basis. Individual cache entries are evicted after their expiration time has passed. The periodic nature of eviction means that cache entries tend to survive around (expirationTime + (evictionInterval / 2))
In addition, when the cache is full, adding a new item will displace the item that has been referenced least recently.
defaultExpiration specifies the default minimum amount of time a cached entry remains in the cache before eviction. This value is used with the Set function. Explicit per-entry expiration times can be set with the SetWithExpiration function instead.
evictionInterval specifies the frequency at which eviction activities take place. This should likely be >= 1 second.
func NewTTL ¶
func NewTTL(defaultExpiration time.Duration, evictionInterval time.Duration) ExpiringCache
NewTTL creates a new cache with a time-based eviction model.
Cache eviction is done on a periodic basis. Individual cache entries are evicted after their expiration time has passed. The periodic nature of eviction means that cache entries tend to survive around (expirationTime + (evictionInterval / 2))
defaultExpiration specifies the default minimum amount of time a cached entry remains in the cache before eviction. This value is used with the Set function. Explicit per-entry expiration times can be set with the SetWithExpiration function instead.
evictionInterval specifies the frequency at which eviction activities take place. This should likely be >= 1 second.
Since TTL caches only evict data based on the passage of time, it's possible to use up all available memory by continuing to add entries to the cache with a long enough expiration time. Don't do that.
func NewTTLWithCallback ¶
func NewTTLWithCallback(defaultExpiration time.Duration, evictionInterval time.Duration, callback EvictionCallback) ExpiringCache
NewTTLWithCallback creates a new cache with a time-based eviction model that will invoke the supplied callback on all evictions. See also: NewTTL.
type Stats ¶
type Stats struct {
// Writes captures the number of times state in the cache was added or updated.
Writes uint64
// Hits captures the number of times a Get operation succeeded to find an entry in the cache.
Hits uint64
// Misses captures the number of times a Get operation failed to find an entry in the cache.
Misses uint64
// Evictions captures the number of entries that have been evicted from the cache
Evictions uint64
// Removals captures the number of entries that have been explicitly removed from the
// cache
Removals uint64
}
Stats returns usage statistics about an individual cache, useful to assess the efficiency of a cache.
The values returned in this struct are approximations of the current state of the cache. For the sake of efficiency, certain edge cases in the implementation can lead to inaccuracies.
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