cache

Documentation

Overview

Package cache implements a LRU cache.

The implementation borrows heavily from SmallLRUCache (originally by Nathan Schrenk). The object maintains a doubly-linked list of elements. When an element is accessed, it is promoted to the head of the list. When space is needed, the element at the tail of the list (the least recently used element) is evicted.

Index

• Variables
• func NewRistrettoCache(maxEntries, maxCost int64, cost func(any) int64) *ristretto.Cache
• type Cache
  • func NewDefaultCacheImpl(cfg *Config) Cache
• type Config
• type Item
• type LRUCache
  • func NewLRUCache(capacity int64, cost func(any) int64) *LRUCache
  • func (lru *LRUCache) Clear()
  • func (lru *LRUCache) Delete(key string)
  • func (lru *LRUCache) Evictions() int64
  • func (lru *LRUCache) ForEach(callback func(value any) bool)
  • func (lru *LRUCache) Get(key string) (v any, ok bool)
  • func (lru *LRUCache) Hits() int64
  • func (lru *LRUCache) Items() []Item
  • func (lru *LRUCache) Len() int
  • func (lru *LRUCache) MaxCapacity() int64
  • func (lru *LRUCache) Misses() int64
  • func (lru *LRUCache) Set(key string, value any) bool
  • func (lru *LRUCache) SetCapacity(capacity int64)
  • func (lru *LRUCache) UsedCapacity() int64
  • func (lru *LRUCache) Wait()

Variables

var DefaultConfig = &Config{
	MaxEntries:     5000,
	MaxMemoryUsage: 32 * 1024 * 1024,
	LFU:            true,
}

DefaultConfig is the default configuration for a cache instance in Vitess

Functions

func NewRistrettoCache

func NewRistrettoCache(maxEntries, maxCost int64, cost func(any) int64) *ristretto.Cache

NewRistrettoCache returns a Cache implementation based on Ristretto

Types

type Cache

type Cache interface {
	Get(key string) (any, bool)
	Set(key string, val any) bool
	ForEach(callback func(any) bool)

	Delete(key string)
	Clear()

	// Wait waits for all pending operations on the cache to settle. Since cache writes
	// are asynchronous, a write may not be immediately accessible unless the user
	// manually calls Wait.
	Wait()

	Len() int
	Evictions() int64
	Hits() int64
	Misses() int64
	UsedCapacity() int64
	MaxCapacity() int64
	SetCapacity(int64)
}

Cache is a generic interface type for a data structure that keeps recently used objects in memory and evicts them when it becomes full.

func NewDefaultCacheImpl

func NewDefaultCacheImpl(cfg *Config) Cache

NewDefaultCacheImpl returns the default cache implementation for Vitess. The options in the Config struct control the memory and entry limits for the cache, and the underlying cache implementation.

type Config

type Config struct {
	// MaxEntries is the estimated amount of entries that the cache will hold at capacity
	MaxEntries int64
	// MaxMemoryUsage is the maximum amount of memory the cache can handle
	MaxMemoryUsage int64
	// LFU toggles whether to use a new cache implementation with a TinyLFU admission policy
	LFU bool
}

Config is the configuration options for a cache instance

type Item

type Item struct {
	Key   string
	Value any
}

Item is what is stored in the cache

type LRUCache

type LRUCache struct {
	// contains filtered or unexported fields
}

LRUCache is a typical LRU cache implementation. If the cache reaches the capacity, the least recently used item is deleted from the cache. Note the capacity is not the number of items, but the total sum of the CachedSize() of each item.

func NewLRUCache

func NewLRUCache(capacity int64, cost func(any) int64) *LRUCache

NewLRUCache creates a new empty cache with the given capacity.

func (*LRUCache) Clear

func (lru *LRUCache) Clear()

Clear will clear the entire cache.

func (*LRUCache) Delete

func (lru *LRUCache) Delete(key string)

Delete removes an entry from the cache

func (*LRUCache) Evictions

func (lru *LRUCache) Evictions() int64

Evictions returns the number of evictions

func (*LRUCache) ForEach

func (lru *LRUCache) ForEach(callback func(value any) bool)

ForEach yields all the values for the cache, ordered from most recently used to least recently used.

func (*LRUCache) Get

func (lru *LRUCache) Get(key string) (v any, ok bool)

Get returns a value from the cache, and marks the entry as most recently used.

func (*LRUCache) Hits

func (lru *LRUCache) Hits() int64

Hits returns number of cache hits since creation

func (*LRUCache) Items

func (lru *LRUCache) Items() []Item

Items returns all the values for the cache, ordered from most recently used to least recently used.

func (*LRUCache) Len

func (lru *LRUCache) Len() int

Len returns the size of the cache (in entries)

func (*LRUCache) MaxCapacity

func (lru *LRUCache) MaxCapacity() int64

MaxCapacity returns the cache maximum capacity.

func (*LRUCache) Misses

func (lru *LRUCache) Misses() int64

Misses returns number of cache misses since creation

func (*LRUCache) Set

func (lru *LRUCache) Set(key string, value any) bool

Set sets a value in the cache.

func (*LRUCache) SetCapacity

func (lru *LRUCache) SetCapacity(capacity int64)

SetCapacity will set the capacity of the cache. If the capacity is smaller, and the current cache size exceed that capacity, the cache will be shrank.

func (*LRUCache) UsedCapacity

func (lru *LRUCache) UsedCapacity() int64

UsedCapacity returns the size of the cache (in bytes)

func (*LRUCache) Wait

func (lru *LRUCache) Wait()

Wait is a no-op in the LRU cache