From aaafafbdfe07754b771b824c71034f65c77cc76e Mon Sep 17 00:00:00 2001 From: Dimitri Sokolyuk Date: Wed, 25 Jul 2018 09:18:08 +0200 Subject: add title caching --- vendor/github.com/hashicorp/golang-lru/arc.go | 257 ++++++++++++++++++++++++++ 1 file changed, 257 insertions(+) create mode 100644 vendor/github.com/hashicorp/golang-lru/arc.go (limited to 'vendor/github.com/hashicorp/golang-lru/arc.go') diff --git a/vendor/github.com/hashicorp/golang-lru/arc.go b/vendor/github.com/hashicorp/golang-lru/arc.go new file mode 100644 index 0000000..555225a --- /dev/null +++ b/vendor/github.com/hashicorp/golang-lru/arc.go @@ -0,0 +1,257 @@ +package lru + +import ( + "sync" + + "github.com/hashicorp/golang-lru/simplelru" +) + +// 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. +type ARCCache struct { + size int // Size is the total capacity of the cache + p int // P is the dynamic preference towards T1 or T2 + + t1 simplelru.LRUCache // T1 is the LRU for recently accessed items + b1 simplelru.LRUCache // B1 is the LRU for evictions from t1 + + t2 simplelru.LRUCache // T2 is the LRU for frequently accessed items + b2 simplelru.LRUCache // B2 is the LRU for evictions from t2 + + lock sync.RWMutex +} + +// NewARC creates an ARC of the given size +func NewARC(size int) (*ARCCache, error) { + // Create the sub LRUs + b1, err := simplelru.NewLRU(size, nil) + if err != nil { + return nil, err + } + b2, err := simplelru.NewLRU(size, nil) + if err != nil { + return nil, err + } + t1, err := simplelru.NewLRU(size, nil) + if err != nil { + return nil, err + } + t2, err := simplelru.NewLRU(size, nil) + if err != nil { + return nil, err + } + + // Initialize the ARC + c := &ARCCache{ + size: size, + p: 0, + t1: t1, + b1: b1, + t2: t2, + b2: b2, + } + return c, nil +} + +// Get looks up a key's value from the cache. +func (c *ARCCache) Get(key interface{}) (value interface{}, ok bool) { + c.lock.Lock() + defer c.lock.Unlock() + + // If the value is contained in T1 (recent), then + // promote it to T2 (frequent) + if val, ok := c.t1.Peek(key); ok { + c.t1.Remove(key) + c.t2.Add(key, val) + return val, ok + } + + // Check if the value is contained in T2 (frequent) + if val, ok := c.t2.Get(key); ok { + return val, ok + } + + // No hit + return nil, false +} + +// Add adds a value to the cache. +func (c *ARCCache) Add(key, value interface{}) { + c.lock.Lock() + defer c.lock.Unlock() + + // Check if the value is contained in T1 (recent), and potentially + // promote it to frequent T2 + if c.t1.Contains(key) { + c.t1.Remove(key) + c.t2.Add(key, value) + return + } + + // Check if the value is already in T2 (frequent) and update it + if c.t2.Contains(key) { + c.t2.Add(key, value) + return + } + + // Check if this value was recently evicted as part of the + // recently used list + if c.b1.Contains(key) { + // T1 set is too small, increase P appropriately + delta := 1 + b1Len := c.b1.Len() + b2Len := c.b2.Len() + if b2Len > b1Len { + delta = b2Len / b1Len + } + if c.p+delta >= c.size { + c.p = c.size + } else { + c.p += delta + } + + // Potentially need to make room in the cache + if c.t1.Len()+c.t2.Len() >= c.size { + c.replace(false) + } + + // Remove from B1 + c.b1.Remove(key) + + // Add the key to the frequently used list + c.t2.Add(key, value) + return + } + + // Check if this value was recently evicted as part of the + // frequently used list + if c.b2.Contains(key) { + // T2 set is too small, decrease P appropriately + delta := 1 + b1Len := c.b1.Len() + b2Len := c.b2.Len() + if b1Len > b2Len { + delta = b1Len / b2Len + } + if delta >= c.p { + c.p = 0 + } else { + c.p -= delta + } + + // Potentially need to make room in the cache + if c.t1.Len()+c.t2.Len() >= c.size { + c.replace(true) + } + + // Remove from B2 + c.b2.Remove(key) + + // Add the key to the frequently used list + c.t2.Add(key, value) + return + } + + // Potentially need to make room in the cache + if c.t1.Len()+c.t2.Len() >= c.size { + c.replace(false) + } + + // Keep the size of the ghost buffers trim + if c.b1.Len() > c.size-c.p { + c.b1.RemoveOldest() + } + if c.b2.Len() > c.p { + c.b2.RemoveOldest() + } + + // Add to the recently seen list + c.t1.Add(key, value) + return +} + +// replace is used to adaptively evict from either T1 or T2 +// based on the current learned value of P +func (c *ARCCache) replace(b2ContainsKey bool) { + t1Len := c.t1.Len() + if t1Len > 0 && (t1Len > c.p || (t1Len == c.p && b2ContainsKey)) { + k, _, ok := c.t1.RemoveOldest() + if ok { + c.b1.Add(k, nil) + } + } else { + k, _, ok := c.t2.RemoveOldest() + if ok { + c.b2.Add(k, nil) + } + } +} + +// Len returns the number of cached entries +func (c *ARCCache) Len() int { + c.lock.RLock() + defer c.lock.RUnlock() + return c.t1.Len() + c.t2.Len() +} + +// Keys returns all the cached keys +func (c *ARCCache) Keys() []interface{} { + c.lock.RLock() + defer c.lock.RUnlock() + k1 := c.t1.Keys() + k2 := c.t2.Keys() + return append(k1, k2...) +} + +// Remove is used to purge a key from the cache +func (c *ARCCache) Remove(key interface{}) { + c.lock.Lock() + defer c.lock.Unlock() + if c.t1.Remove(key) { + return + } + if c.t2.Remove(key) { + return + } + if c.b1.Remove(key) { + return + } + if c.b2.Remove(key) { + return + } +} + +// Purge is used to clear the cache +func (c *ARCCache) Purge() { + c.lock.Lock() + defer c.lock.Unlock() + c.t1.Purge() + c.t2.Purge() + c.b1.Purge() + c.b2.Purge() +} + +// Contains is used to check if the cache contains a key +// without updating recency or frequency. +func (c *ARCCache) Contains(key interface{}) bool { + c.lock.RLock() + defer c.lock.RUnlock() + return c.t1.Contains(key) || c.t2.Contains(key) +} + +// Peek is used to inspect the cache value of a key +// without updating recency or frequency. +func (c *ARCCache) Peek(key interface{}) (value interface{}, ok bool) { + c.lock.RLock() + defer c.lock.RUnlock() + if val, ok := c.t1.Peek(key); ok { + return val, ok + } + return c.t2.Peek(key) +} -- cgit v1.2.3