README
¶
BigCache 
Fast, concurrent, evicting in-memory cache written to keep big number of entries without impact on performance. BigCache keeps entries on heap but omits GC for them. To achieve that operations on bytes arrays take place, therefore entries (de)serialization in front of the cache will be needed in most use cases.
Usage
Simple initialization
import "github.com/allegro/bigcache"
cache, _ := bigcache.NewBigCache(bigcache.DefaultConfig(10 * time.Minute))
cache.Set("my-unique-key", []byte("value"))
entry, _ := cache.Get("my-unique-key")
fmt.Println(string(entry))
Custom initialization
When cache load can be predicted in advance then it is better to use custom initialization because additional memory allocation can be avoided in that way.
import (
"log"
"github.com/allegro/bigcache"
)
config := bigcache.Config {
// number of shards (must be a power of 2)
Shards: 1024,
// time after which entry can be evicted
LifeWindow: 10 * time.Minute,
// rps * lifeWindow, used only in initial memory allocation
MaxEntriesInWindow: 1000 * 10 * 60,
// max entry size in bytes, used only in initial memory allocation
MaxEntrySize: 500,
// prints information about additional memory allocation
Verbose: true,
// cache will not allocate more memory than this limit, value in MB
// if value is reached then the oldest entries can be overridden for the new ones
// 0 value means no size limit
HardMaxCacheSize: 8192,
// callback fired when the oldest entry is removed because of its
// expiration time or no space left for the new entry. Default value is nil which
// means no callback and it prevents from unwrapping the oldest entry.
OnRemove: nil,
}
cache, initErr := bigcache.NewBigCache(config)
if initErr != nil {
log.Fatal(initErr)
}
cache.Set("my-unique-key", []byte("value"))
if entry, err := cache.Get("my-unique-key"); err == nil {
fmt.Println(string(entry))
}
Benchmarks
Three caches were compared: bigcache, freecache and map. Benchmark tests were made on MacBook Pro (3 GHz Processor Intel Core i7, 16GB Memory).
Writes and reads
cd caches_bench; go test -bench=. -benchtime=10s ./... -timeout 30m
BenchmarkMapSet-4 20000000 1681 ns/op 296 B/op 3 allocs/op
BenchmarkFreeCacheSet-4 20000000 1132 ns/op 349 B/op 3 allocs/op
BenchmarkBigCacheSet-4 20000000 831 ns/op 305 B/op 2 allocs/op
BenchmarkMapGet-4 30000000 540 ns/op 24 B/op 2 allocs/op
BenchmarkFreeCacheGet-4 20000000 986 ns/op 152 B/op 4 allocs/op
BenchmarkBigCacheGet-4 20000000 726 ns/op 40 B/op 3 allocs/op
BenchmarkBigCacheSetParallel-4 20000000 532 ns/op 313 B/op 3 allocs/op
BenchmarkFreeCacheSetParallel-4 20000000 564 ns/op 357 B/op 4 allocs/op
BenchmarkBigCacheGetParallel-4 50000000 338 ns/op 40 B/op 3 allocs/op
BenchmarkFreeCacheGetParallel-4 30000000 581 ns/op 152 B/op 4 allocs/op
Writes and reads in bigcache are faster than in freecache. Writes to map are the slowest.
GC pause time
cd caches_bench; go run caches_gc_overhead_comparison.go
Number of entries: 20000000
GC pause for bigcache: 27.81671ms
GC pause for freecache: 30.218371ms
GC pause for map: 11.590772251s
Test shows how long are the GC pauses for caches filled with 20mln of entries. Bigcache and freecache have very similar GC pause time. It is clear that both reduce GC overhead in contrast to map which GC pause time took more than 10 seconds.
How it works
BigCache relies on optimization presented in 1.5 version of Go (issue-9477).
This optimization states that if map without pointers in keys and values is used then GC will omit it’s content.
Therefore BigCache uses map[uint64]uint32 where keys are hashed and values are offsets of entries.
Entries are kept in bytes array, to omit GC again. Bytes array size can grow to gigabytes without impact on performance because GC will only see single pointer to it.
Bigcache vs Freecache
Both caches provide the same core features but they reduce GC overhead in different ways.
Bigcache relies on map[uint64]uint32, freecache implements its own mapping built on
slices to reduce number of pointers.
Results from benchmark tests are presented above. One of the advantage of bigcache over freecache is that you don’t need to know the size of the cache in advance, because when bigcache is full, it can allocate additional memory for new entries instead of overwriting existing ones as freecache does currently. However hard max size in bigcache also can be set, check HardMaxCacheSize.
More
Bigcache genesis is described in allegro.tech blog post: writing a very fast cache service in Go
License
BigCache is released under the Apache 2.0 license (see LICENSE)
Documentation
¶
Index ¶
Constants ¶
const ErrCannotRetrieveEntry = iteratorError("Could not retrieve entry from cache")
ErrCannotRetrieveEntry is reported when entry cannot be retrieved from underlying
const ErrInvalidIteratorState = iteratorError("Iterator is in invalid state. Use SetNext() to move to next position")
ErrInvalidIteratorState is reported when iterator is in invalid state
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type BigCache ¶
type BigCache struct {
// contains filtered or unexported fields
}
BigCache is fast, concurrent, evicting cache created to keep big number of entries without impact on performance. It keeps entries on heap but omits GC for them. To achieve that operations on bytes arrays take place, therefore entries (de)serialization in front of the cache will be needed in most use cases.
func NewBigCache ¶
NewBigCache initialize new instance of BigCache
func (*BigCache) Iterator ¶
func (c *BigCache) Iterator() *EntryInfoIterator
Iterator returns iterator function to iterate over EntryInfo's from whole cache.
type Config ¶
type Config struct {
// Number of cache shards, value must be a power of two
Shards int
// Time after which entry can be evicted
LifeWindow time.Duration
// Interval between removing expired entries (clean up).
// If set to <= 0 then no action is performed. Setting to < 1 second is counterproductive — bigcache has a one second resolution.
CleanWindow time.Duration
// Max number of entries in life window. Used only to calculate initial size for cache shards.
// When proper value is set then additional memory allocation does not occur.
MaxEntriesInWindow int
// Max size of entry in bytes. Used only to calculate initial size for cache shards.
MaxEntrySize int
// Verbose mode prints information about new memory allocation
Verbose bool
// Hasher used to map between string keys and unsigned 64bit integers, by default fnv64 hashing is used.
Hasher Hasher
// HardMaxCacheSize is a limit for cache size in MB. Cache will not allocate more memory than this limit.
// It can protect application from consuming all available memory on machine, therefore from running OOM Killer.
// Default value is 0 which means unlimited size. When the limit is higher than 0 and reached then
// the oldest entries are overridden for the new ones.
HardMaxCacheSize int
// OnRemove is a callback fired when the oldest entry is removed because of its expiration time or no space left
// for the new entry. Default value is nil which means no callback and it prevents from unwrapping the oldest entry.
OnRemove func(key string, entry []byte)
}
Config for BigCache
func DefaultConfig ¶
DefaultConfig initializes config with default values. When load for BigCache can be predicted in advance then it is better to use custom config.
type EntryInfo ¶
type EntryInfo struct {
// contains filtered or unexported fields
}
EntryInfo holds informations about entry in the cache
type EntryInfoIterator ¶
type EntryInfoIterator struct {
// contains filtered or unexported fields
}
EntryInfoIterator allows to iterate over entries in the cache
func (*EntryInfoIterator) SetNext ¶
func (it *EntryInfoIterator) SetNext() bool
SetNext moves to next element and returns true if it exists.
func (*EntryInfoIterator) Value ¶
func (it *EntryInfoIterator) Value() (EntryInfo, error)
Value returns current value from the iterator
type EntryNotFoundError ¶
type EntryNotFoundError struct {
// contains filtered or unexported fields
}
EntryNotFoundError is an error type struct which is returned when entry was not found for provided key
func (EntryNotFoundError) Error ¶
func (e EntryNotFoundError) Error() string
Error returned when entry does not exist.
Source Files
Directories