mirror of
https://github.com/VictoriaMetrics/VictoriaMetrics.git
synced 2024-12-20 23:46:23 +01:00
411 lines
9.5 KiB
Go
411 lines
9.5 KiB
Go
package blockcache
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import (
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"container/heap"
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"sync"
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"sync/atomic"
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"time"
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"unsafe"
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"github.com/VictoriaMetrics/VictoriaMetrics/lib/cgroup"
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"github.com/VictoriaMetrics/VictoriaMetrics/lib/fasttime"
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"github.com/cespare/xxhash/v2"
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)
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// Cache caches Block entries.
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//
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// Call NewCache() for creating new Cache.
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type Cache struct {
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shards []*cache
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cleanerMustStopCh chan struct{}
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cleanerStoppedCh chan struct{}
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}
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// NewCache creates new cache.
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//
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// Cache size in bytes is limited by the value returned by getMaxSizeBytes() callback.
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// Call MustStop() in order to free up resources occupied by Cache.
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func NewCache(getMaxSizeBytes func() int) *Cache {
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cpusCount := cgroup.AvailableCPUs()
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shardsCount := cgroup.AvailableCPUs()
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// Increase the number of shards with the increased number of available CPU cores.
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// This should reduce contention on per-shard mutexes.
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multiplier := cpusCount
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if multiplier > 16 {
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multiplier = 16
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}
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shardsCount *= multiplier
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shards := make([]*cache, shardsCount)
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getMaxShardBytes := func() int {
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n := getMaxSizeBytes()
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return n / shardsCount
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}
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for i := range shards {
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shards[i] = newCache(getMaxShardBytes)
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}
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c := &Cache{
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shards: shards,
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cleanerMustStopCh: make(chan struct{}),
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cleanerStoppedCh: make(chan struct{}),
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}
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go c.cleaner()
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return c
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}
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// MustStop frees up resources occupied by c.
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func (c *Cache) MustStop() {
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close(c.cleanerMustStopCh)
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<-c.cleanerStoppedCh
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}
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// RemoveBlocksForPart removes all the blocks for the given part from the cache.
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func (c *Cache) RemoveBlocksForPart(p interface{}) {
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for _, shard := range c.shards {
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shard.RemoveBlocksForPart(p)
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}
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}
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// GetBlock returns a block for the given key k from c.
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func (c *Cache) GetBlock(k Key) Block {
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idx := uint64(0)
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if len(c.shards) > 1 {
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h := k.hashUint64()
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idx = h % uint64(len(c.shards))
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}
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shard := c.shards[idx]
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return shard.GetBlock(k)
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}
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// PutBlock puts the given block b under the given key k into c.
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func (c *Cache) PutBlock(k Key, b Block) {
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idx := uint64(0)
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if len(c.shards) > 1 {
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h := k.hashUint64()
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idx = h % uint64(len(c.shards))
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}
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shard := c.shards[idx]
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shard.PutBlock(k, b)
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}
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// Len returns the number of blocks in the cache c.
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func (c *Cache) Len() int {
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n := 0
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for _, shard := range c.shards {
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n += shard.Len()
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}
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return n
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}
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// SizeBytes returns an approximate size in bytes of all the blocks stored in the cache c.
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func (c *Cache) SizeBytes() int {
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n := 0
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for _, shard := range c.shards {
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n += shard.SizeBytes()
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}
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return n
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}
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// SizeMaxBytes returns the max allowed size in bytes for c.
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func (c *Cache) SizeMaxBytes() int {
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n := 0
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for _, shard := range c.shards {
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n += shard.SizeMaxBytes()
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}
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return n
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}
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// Requests returns the number of requests served by c.
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func (c *Cache) Requests() uint64 {
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n := uint64(0)
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for _, shard := range c.shards {
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n += shard.Requests()
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}
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return n
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}
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// Misses returns the number of cache misses for c.
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func (c *Cache) Misses() uint64 {
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n := uint64(0)
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for _, shard := range c.shards {
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n += shard.Misses()
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}
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return n
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}
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func (c *Cache) cleaner() {
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ticker := time.NewTicker(57 * time.Second)
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defer ticker.Stop()
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perKeyMissesTicker := time.NewTicker(3 * time.Minute)
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defer perKeyMissesTicker.Stop()
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for {
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select {
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case <-c.cleanerMustStopCh:
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close(c.cleanerStoppedCh)
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return
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case <-ticker.C:
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c.cleanByTimeout()
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case <-perKeyMissesTicker.C:
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c.cleanPerKeyMisses()
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}
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}
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}
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func (c *Cache) cleanByTimeout() {
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for _, shard := range c.shards {
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shard.cleanByTimeout()
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}
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}
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func (c *Cache) cleanPerKeyMisses() {
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for _, shard := range c.shards {
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shard.cleanPerKeyMisses()
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}
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}
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type cache struct {
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// Atomically updated fields must go first in the struct, so they are properly
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// aligned to 8 bytes on 32-bit architectures.
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// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/212
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requests uint64
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misses uint64
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// sizeBytes contains an approximate size for all the blocks stored in the cache.
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sizeBytes int64
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// getMaxSizeBytes() is a callback, which returns the maximum allowed cache size in bytes.
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getMaxSizeBytes func() int
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// mu protects all the fields below.
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mu sync.Mutex
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// m contains cached blocks keyed by Key.Part and then by Key.Offset
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m map[interface{}]map[uint64]*cacheEntry
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// perKeyMisses contains per-block cache misses.
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//
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// Blocks with less than 2 cache misses aren't stored in the cache in order to prevent from eviction for frequently accessed items.
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perKeyMisses map[Key]int
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// The heap for removing the least recently used entries from m.
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lah lastAccessHeap
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}
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// Key represents a key, which uniquely identifies the Block.
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type Key struct {
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// Part must contain a pointer to part structure where the block belongs to.
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Part interface{}
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// Offset is the offset of the block in the part.
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Offset uint64
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}
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func (k *Key) hashUint64() uint64 {
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buf := (*[unsafe.Sizeof(*k)]byte)(unsafe.Pointer(k))
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return xxhash.Sum64(buf[:])
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}
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// Block is an item, which may be cached in the Cache.
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type Block interface {
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// SizeBytes must return the approximate size of the given block in bytes
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SizeBytes() int
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}
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type cacheEntry struct {
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// The timestamp in seconds for the last access to the given entry.
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lastAccessTime uint64
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// heapIdx is the index for the entry in lastAccessHeap.
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heapIdx int
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// k contains the associated key for the given block.
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k Key
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// b contains the cached block.
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b Block
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}
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func newCache(getMaxSizeBytes func() int) *cache {
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var c cache
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c.getMaxSizeBytes = getMaxSizeBytes
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c.m = make(map[interface{}]map[uint64]*cacheEntry)
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c.perKeyMisses = make(map[Key]int)
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return &c
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}
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func (c *cache) RemoveBlocksForPart(p interface{}) {
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c.mu.Lock()
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defer c.mu.Unlock()
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sizeBytes := 0
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for _, e := range c.m[p] {
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sizeBytes += e.b.SizeBytes()
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heap.Remove(&c.lah, e.heapIdx)
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// do not delete the entry from c.perKeyMisses, since it is removed by cache.cleaner later.
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}
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c.updateSizeBytes(-sizeBytes)
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delete(c.m, p)
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}
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func (c *cache) updateSizeBytes(n int) {
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atomic.AddInt64(&c.sizeBytes, int64(n))
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}
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func (c *cache) cleanPerKeyMisses() {
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c.mu.Lock()
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c.perKeyMisses = make(map[Key]int, len(c.perKeyMisses))
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c.mu.Unlock()
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}
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func (c *cache) cleanByTimeout() {
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// Delete items accessed more than three minutes ago.
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// This time should be enough for repeated queries.
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lastAccessTime := fasttime.UnixTimestamp() - 3*60
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c.mu.Lock()
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defer c.mu.Unlock()
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for len(c.lah) > 0 {
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if lastAccessTime < c.lah[0].lastAccessTime {
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break
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}
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c.removeLeastRecentlyAccessedItem()
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}
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}
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func (c *cache) GetBlock(k Key) Block {
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atomic.AddUint64(&c.requests, 1)
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var e *cacheEntry
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c.mu.Lock()
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defer c.mu.Unlock()
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pes := c.m[k.Part]
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if pes != nil {
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e = pes[k.Offset]
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if e != nil {
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// Fast path - the block already exists in the cache, so return it to the caller.
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currentTime := fasttime.UnixTimestamp()
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if e.lastAccessTime != currentTime {
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e.lastAccessTime = currentTime
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heap.Fix(&c.lah, e.heapIdx)
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}
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return e.b
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}
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}
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// Slow path - the entry is missing in the cache.
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c.perKeyMisses[k]++
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atomic.AddUint64(&c.misses, 1)
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return nil
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}
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func (c *cache) PutBlock(k Key, b Block) {
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c.mu.Lock()
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defer c.mu.Unlock()
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// If the entry wasn't accessed yet (e.g. c.perKeyMisses[k] == 0), then cache it, since it is likely it will be accessed soon.
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// Do not cache the entry only if there was only a single unsuccessful attempt to access it.
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// This may be one-time-wonders entry, which won't be accessed more, so there is no need in caching it.
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doNotCache := c.perKeyMisses[k] == 1
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if doNotCache {
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// Do not cache b if it has been requested only once (aka one-time-wonders items).
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// This should reduce memory usage for the cache.
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return
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}
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// Store b in the cache.
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pes := c.m[k.Part]
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if pes == nil {
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pes = make(map[uint64]*cacheEntry)
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c.m[k.Part] = pes
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} else if pes[k.Offset] != nil {
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// The block has been already registered by concurrent goroutine.
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return
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}
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e := &cacheEntry{
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lastAccessTime: fasttime.UnixTimestamp(),
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k: k,
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b: b,
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}
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heap.Push(&c.lah, e)
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pes[k.Offset] = e
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c.updateSizeBytes(e.b.SizeBytes())
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maxSizeBytes := c.getMaxSizeBytes()
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for c.SizeBytes() > maxSizeBytes && len(c.lah) > 0 {
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c.removeLeastRecentlyAccessedItem()
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}
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}
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func (c *cache) removeLeastRecentlyAccessedItem() {
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e := c.lah[0]
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c.updateSizeBytes(-e.b.SizeBytes())
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p := e.k.Part
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pes := c.m[p]
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delete(pes, e.k.Offset)
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if len(pes) == 0 {
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// Remove reference to p from c.m in order to free up memory occupied by p.
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delete(c.m, p)
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}
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heap.Pop(&c.lah)
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}
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func (c *cache) Len() int {
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c.mu.Lock()
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defer c.mu.Unlock()
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n := 0
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for _, m := range c.m {
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n += len(m)
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}
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return n
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}
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func (c *cache) SizeBytes() int {
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return int(atomic.LoadInt64(&c.sizeBytes))
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}
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func (c *cache) SizeMaxBytes() int {
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return c.getMaxSizeBytes()
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}
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func (c *cache) Requests() uint64 {
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return atomic.LoadUint64(&c.requests)
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}
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func (c *cache) Misses() uint64 {
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return atomic.LoadUint64(&c.misses)
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}
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// lastAccessHeap implements heap.Interface
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type lastAccessHeap []*cacheEntry
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func (lah *lastAccessHeap) Len() int {
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return len(*lah)
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}
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func (lah *lastAccessHeap) Swap(i, j int) {
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h := *lah
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a := h[i]
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b := h[j]
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a.heapIdx = j
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b.heapIdx = i
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h[i] = b
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h[j] = a
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}
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func (lah *lastAccessHeap) Less(i, j int) bool {
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h := *lah
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return h[i].lastAccessTime < h[j].lastAccessTime
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}
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func (lah *lastAccessHeap) Push(x interface{}) {
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e := x.(*cacheEntry)
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h := *lah
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e.heapIdx = len(h)
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*lah = append(h, e)
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}
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func (lah *lastAccessHeap) Pop() interface{} {
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h := *lah
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e := h[len(h)-1]
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// Remove the reference to deleted entry, so Go GC could free up memory occupied by the deleted entry.
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h[len(h)-1] = nil
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*lah = h[:len(h)-1]
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return e
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}
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