lru

README

golang-lru

This provides the lru package which implements a fixed-size thread safe LRU cache. It is based on the cache in Groupcache.

It is a fork of the non-generic golang-lru from Hashicorp. The intetion is to track upstream closely, porting over generic typings.

Documentation

Full docs are available on Godoc

Example

Using the LRU is very simple:

l, _ := New[int, int](128)
for i := 0; i < 256; i++ {
    l.Add(i, nil)
}
if l.Len() != 128 {
    panic(fmt.Sprintf("bad len: %v", l.Len()))
}

Supported Go Versions

Following the standard Go version support policy, this package will support the last two versions of Go that support generics.

Documentation

Overview

Package lru provides three different LRU caches of varying sophistication.

Cache is a simple LRU cache. It is based on the LRU implementation in groupcache: https://github.com/golang/groupcache/tree/master/lru

TwoQueueCache tracks frequently used and recently used entries separately. This avoids a burst of accesses from taking out frequently used entries, at the cost of about 2x computational overhead and some extra bookkeeping.

ARCCache is an adaptive replacement cache. It tracks recent evictions as well as recent usage in both the frequent and recent caches. Its computational overhead is comparable to TwoQueueCache, but the memory overhead is linear with the size of the cache.

ARC has been patented by IBM, so do not use it if that is problematic for your program.

All caches in this package take locks while operating, and are therefore thread-safe for consumers.

Index

• Constants
• type ARCCache
  • func NewARC[Key comparable, Value any](size int) (*ARCCache[Key, Value], error)
  • func (c *ARCCache[Key, Value]) Add(key Key, value Value)
  • func (c *ARCCache[Key, Value]) Contains(key Key) bool
  • func (c *ARCCache[Key, Value]) Get(key Key) (value Value, ok bool)
  • func (c *ARCCache[Key, Value]) Keys() []Key
  • func (c *ARCCache[Key, Value]) Len() int
  • func (c *ARCCache[Key, Value]) Peek(key Key) (value Value, ok bool)
  • func (c *ARCCache[Key, Value]) Purge()
  • func (c *ARCCache[Key, Value]) Remove(key Key)
• type Cache
  • func New[Key comparable, Value any](size int) (*Cache[Key, Value], error)
  • func NewWithEvict[Key comparable, Value any](size int, onEvicted func(key Key, value Value)) (c *Cache[Key, Value], err error)
  • func (c *Cache[Key, Value]) Add(key Key, value Value) (evicted bool)
  • func (c *Cache[Key, Value]) Contains(key Key) bool
  • func (c *Cache[Key, Value]) ContainsOrAdd(key Key, value Value) (ok, evicted bool)
  • func (c *Cache[Key, Value]) Get(key Key) (value Value, ok bool)
  • func (c *Cache[Key, Value]) GetOldest() (key Key, value Value, ok bool)
  • func (c *Cache[Key, Value]) Keys() []Key
  • func (c *Cache[Key, Value]) Len() int
  • func (c *Cache[Key, Value]) Peek(key Key) (value Value, ok bool)
  • func (c *Cache[Key, Value]) PeekOrAdd(key Key, value Value) (previous Value, ok, evicted bool)
  • func (c *Cache[Key, Value]) Purge()
  • func (c *Cache[Key, Value]) Remove(key Key) (present bool)
  • func (c *Cache[Key, Value]) RemoveOldest() (key Key, value Value, ok bool)
  • func (c *Cache[Key, Value]) Resize(size int) (evicted int)
• type TwoQueueCache
  • func New2Q[Key comparable, Value any](size int) (*TwoQueueCache[Key, Value], error)
  • func New2QParams[Key comparable, Value any](size int, recentRatio, ghostRatio float64) (*TwoQueueCache[Key, Value], error)
  • func (c *TwoQueueCache[Key, Value]) Add(key Key, value Value)
  • func (c *TwoQueueCache[Key, Value]) Contains(key Key) bool
  • func (c *TwoQueueCache[Key, Value]) Get(key Key) (value Value, ok bool)
  • func (c *TwoQueueCache[Key, Value]) Keys() []Key
  • func (c *TwoQueueCache[Key, Value]) Len() int
  • func (c *TwoQueueCache[Key, Value]) Peek(key Key) (value Value, ok bool)
  • func (c *TwoQueueCache[Key, Value]) Purge()
  • func (c *TwoQueueCache[Key, Value]) Remove(key Key)

Constants

const (
	// Default2QRecentRatio is the ratio of the 2Q cache dedicated
	// to recently added entries that have only been accessed once.
	Default2QRecentRatio = 0.25

	// Default2QGhostEntries is the default ratio of ghost
	// entries kept to track entries recently evicted
	Default2QGhostEntries = 0.50
)

const (
	// DefaultEvictedBufferSize defines the default buffer size to store evicted key/val
	DefaultEvictedBufferSize = 16
)

Types

type ARCCache

type ARCCache[Key, Value any] struct {
	// contains filtered or unexported fields
}

ARCCache is a thread-safe fixed size Adaptive Replacement Cache (ARC). ARC is an enhancement over the standard LRU cache in that tracks both frequency and recency of use. This avoids a burst in access to new entries from evicting the frequently used older entries. It adds some additional tracking overhead to a standard LRU cache, computationally it is roughly 2x the cost, and the extra memory overhead is linear with the size of the cache. ARC has been patented by IBM, but is similar to the TwoQueueCache (2Q) which requires setting parameters.

func NewARC

func NewARC[Key comparable, Value any](size int) (*ARCCache[Key, Value], error)

NewARC creates an ARC of the given size

func (*ARCCache[Key, Value]) Add

func (c *ARCCache[Key, Value]) Add(key Key, value Value)

Add adds a value to the cache.

func (*ARCCache[Key, Value]) Contains

func (c *ARCCache[Key, Value]) Contains(key Key) bool

Contains is used to check if the cache contains a key without updating recency or frequency.

func (*ARCCache[Key, Value]) Get

func (c *ARCCache[Key, Value]) Get(key Key) (value Value, ok bool)

Get looks up a key's value from the cache.

func (*ARCCache[Key, Value]) Keys

func (c *ARCCache[Key, Value]) Keys() []Key

Keys returns all the cached keys

func (*ARCCache[Key, Value]) Len

func (c *ARCCache[Key, Value]) Len() int

Len returns the number of cached entries

func (*ARCCache[Key, Value]) Peek

func (c *ARCCache[Key, Value]) Peek(key Key) (value Value, ok bool)

Peek is used to inspect the cache value of a key without updating recency or frequency.

func (*ARCCache[Key, Value]) Purge

func (c *ARCCache[Key, Value]) Purge()

Purge is used to clear the cache

func (*ARCCache[Key, Value]) Remove

func (c *ARCCache[Key, Value]) Remove(key Key)

Remove is used to purge a key from the cache

type Cache

type Cache[Key comparable, Value any] struct {
	// contains filtered or unexported fields
}

Cache is a thread-safe fixed size LRU cache.

func New

func New[Key comparable, Value any](size int) (*Cache[Key, Value], error)

New creates an LRU of the given size.

func NewWithEvict

func NewWithEvict[Key comparable, Value any](size int, onEvicted func(key Key, value Value)) (c *Cache[Key, Value], err error)

NewWithEvict constructs a fixed size cache with the given eviction callback.

func (*Cache[Key, Value]) Add

func (c *Cache[Key, Value]) Add(key Key, value Value) (evicted bool)

Add adds a value to the cache. Returns true if an eviction occurred.

func (*Cache[Key, Value]) Contains

func (c *Cache[Key, Value]) Contains(key Key) bool

Contains checks if a key is in the cache, without updating the recent-ness or deleting it for being stale.

func (*Cache[Key, Value]) ContainsOrAdd

func (c *Cache[Key, Value]) ContainsOrAdd(key Key, value Value) (ok, evicted bool)

ContainsOrAdd checks if a key is in the cache without updating the recent-ness or deleting it for being stale, and if not, adds the value. Returns whether found and whether an eviction occurred.

func (*Cache[Key, Value]) Get

func (c *Cache[Key, Value]) Get(key Key) (value Value, ok bool)

Get looks up a key's value from the cache.

func (*Cache[Key, Value]) GetOldest

func (c *Cache[Key, Value]) GetOldest() (key Key, value Value, ok bool)

GetOldest returns the oldest entry

func (*Cache[Key, Value]) Keys

func (c *Cache[Key, Value]) Keys() []Key

Keys returns a slice of the keys in the cache, from oldest to newest.

func (*Cache[Key, Value]) Len

func (c *Cache[Key, Value]) Len() int

Len returns the number of items in the cache.

func (*Cache[Key, Value]) Peek

func (c *Cache[Key, Value]) Peek(key Key) (value Value, ok bool)

Peek returns the key value (or undefined if not found) without updating the "recently used"-ness of the key.

func (*Cache[Key, Value]) PeekOrAdd

func (c *Cache[Key, Value]) PeekOrAdd(key Key, value Value) (previous Value, ok, evicted bool)

PeekOrAdd checks if a key is in the cache without updating the recent-ness or deleting it for being stale, and if not, adds the value. Returns whether found and whether an eviction occurred.

func (*Cache[Key, Value]) Purge

func (c *Cache[Key, Value]) Purge()

Purge is used to completely clear the cache.

func (*Cache[Key, Value]) Remove

func (c *Cache[Key, Value]) Remove(key Key) (present bool)

Remove removes the provided key from the cache.

func (*Cache[Key, Value]) RemoveOldest

func (c *Cache[Key, Value]) RemoveOldest() (key Key, value Value, ok bool)

RemoveOldest removes the oldest item from the cache.

func (*Cache[Key, Value]) Resize

func (c *Cache[Key, Value]) Resize(size int) (evicted int)

Resize changes the cache size.

type TwoQueueCache

type TwoQueueCache[Key, Value any] struct {
	// contains filtered or unexported fields
}

TwoQueueCache is a thread-safe fixed size 2Q cache. 2Q is an enhancement over the standard LRU cache in that it tracks both frequently and recently used entries separately. This avoids a burst in access to new entries from evicting frequently used entries. It adds some additional tracking overhead to the standard LRU cache, and is computationally about 2x the cost, and adds some metadata over head. The ARCCache is similar, but does not require setting any parameters.

func New2Q

func New2Q[Key comparable, Value any](size int) (*TwoQueueCache[Key, Value], error)

New2Q creates a new TwoQueueCache using the default values for the parameters.

func New2QParams

func New2QParams[Key comparable, Value any](size int, recentRatio, ghostRatio float64) (*TwoQueueCache[Key, Value], error)

New2QParams creates a new TwoQueueCache using the provided parameter values.

func (*TwoQueueCache[Key, Value]) Add

func (c *TwoQueueCache[Key, Value]) Add(key Key, value Value)

Add adds a value to the cache.

func (*TwoQueueCache[Key, Value]) Contains

func (c *TwoQueueCache[Key, Value]) Contains(key Key) bool

Contains is used to check if the cache contains a key without updating recency or frequency.

func (*TwoQueueCache[Key, Value]) Get

func (c *TwoQueueCache[Key, Value]) Get(key Key) (value Value, ok bool)

Get looks up a key's value from the cache.

func (*TwoQueueCache[Key, Value]) Keys

func (c *TwoQueueCache[Key, Value]) Keys() []Key

Keys returns a slice of the keys in the cache. The frequently used keys are first in the returned slice.

func (*TwoQueueCache[Key, Value]) Len

func (c *TwoQueueCache[Key, Value]) Len() int

Len returns the number of items in the cache.

func (*TwoQueueCache[Key, Value]) Peek

func (c *TwoQueueCache[Key, Value]) Peek(key Key) (value Value, ok bool)

Peek is used to inspect the cache value of a key without updating recency or frequency.

func (*TwoQueueCache[Key, Value]) Purge

func (c *TwoQueueCache[Key, Value]) Purge()

Purge is used to completely clear the cache.

func (*TwoQueueCache[Key, Value]) Remove

func (c *TwoQueueCache[Key, Value]) Remove(key Key)

Remove removes the provided key from the cache.