go内存缓存如何new一个bigcache对象示例详解
作者:海生
这篇文章主要为大家介绍了go内存缓存如何new一个bigcache对象示例详解,有需要的朋友可以借鉴参考下,希望能够有所帮助,祝大家多多进步,早日升职加薪
一、下载源码
在github上,地址https://github.com/allegro/bigcache,我们可以把代码源码clone到本地。
这里选择分支v3.1.0的代码。
二、源码目录
我们打开源码
. ├── LICENSE ├── README.md ├── assert_test.go ├── bigcache.go ├── bigcache_bench_test.go ├── bigcache_test.go ├── bytes.go ├── bytes_appengine.go ├── clock.go ├── config.go ├── encoding.go ├── encoding_test.go ├── entry_not_found_error.go ├── examples_test.go ├── fnv.go ├── fnv_bench_test.go ├── fnv_test.go ├── go.mod ├── go.sum ├── hash.go ├── hash_test.go ├── iterator.go ├── iterator_test.go ├── logger.go ├── queue │ ├── bytes_queue.go │ └── bytes_queue_test.go ├── server │ ├── README.md │ ├── cache_handlers.go │ ├── middleware.go │ ├── middleware_test.go │ ├── server.go │ ├── server_test.go │ └── stats_handler.go ├── shard.go ├── stats.go └── utils.go 2 directories, 36 files
比较重要的几个文件
queue目录
shard.go 分片
fnv.go Fnv hash算法
bigcache.go 初始化new结构体,以及set,get方法。
我们可以看上篇文档的示例:
func TestSetGet(t *testing.T) { // new一个bigCache对象 cache, _ := bigcache.New(context.Background(), bigcache.DefaultConfig(10*time.Minute)) // get获取一个无值的key vNil, err := cache.Get("key") t.Log(vNil, err) // [] Entry not found 值为空的[]字节slice // set 存储数据 cache.Set("key", []byte("value")) // get 获取数据 v, _ := cache.Get("key") t.Log(v) // 输出 [118 97 108 117 101] t.Log(string(v)) // 输出 value }
那么我们先找到这个,第一行对应的
cache, _ := bigcache.New(context.Background(), bigcache.DefaultConfig(10*time.Minute))
在源码的代码如下:
// New initialize new instance of BigCache // New用来初始化一个新的BigCache实例。 func New(ctx context.Context, config Config) (*BigCache, error) { return newBigCache(ctx, config, &systemClock{}) }
我们在使用的时候,主要又涉及到一个 bigcache.DefaultConfig(10*time.Minute))
我们看一下他的方法:
// DefaultConfig initializes config with default values. // DefaultConfig 初始化Config,给定默认值。 // When load for BigCache can be predicted in advance then it is better to use custom config. // 当load加载 BigCache 的时候,如果在使用之前就能预估到使用量,然后预设置config,它好于使用默认config。 func DefaultConfig(eviction time.Duration) Config { return Config{ Shards: 1024, LifeWindow: eviction, CleanWindow: 1 * time.Second, MaxEntriesInWindow: 1000 * 10 * 60, MaxEntrySize: 500, StatsEnabled: false, Verbose: true, Hasher: newDefaultHasher(), HardMaxCacheSize: 0, Logger: DefaultLogger(), } }
设计一个Config结构体
// Config for BigCache type Config struct { // Number of cache shards, value must be a power of two Shards int // Time after which entry can be evicted // LifeWindow后,缓存对象被认为不活跃,但并不会删除对象 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后,会删除被认为不活跃的对象(超过LifeWindow时间的对象),0代表不操作; 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. // 设置最大存储对象数量,仅在初始化时可以设置 MaxEntriesInWindow int // Max size of entry in bytes. Used only to calculate initial size for cache shards. // 缓存对象的最大字节数,仅在初始化时可以设置 MaxEntrySize int // StatsEnabled if true calculate the number of times a cached resource was requested. StatsEnabled bool // Verbose mode prints information about new memory allocation // 是否打印内存分配信息 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 BytesQueue size in MB. // 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. The max memory consumption will be bigger than // HardMaxCacheSize due to Shards' s additional memory. Every Shard consumes additional memory for map of keys // and statistics (map[uint64]uint32) the size of this map is equal to number of entries in // cache ~ 2×(64+32)×n bits + overhead or map itself. // 设置缓存最大值(单位为MB),0表示无限制 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, or because delete was called. // Default value is nil which means no callback and it prevents from unwrapping the oldest entry. // ignored if OnRemoveWithMetadata is specified. // 在缓存过期或者被删除时,可设置回调函数,参数是(key、val),默认是nil不设置 OnRemove func(key string, entry []byte) // OnRemoveWithMetadata is a callback fired when the oldest entry is removed because of its expiration time or no space left // for the new entry, or because delete was called. A structure representing details about that specific entry. // Default value is nil which means no callback and it prevents from unwrapping the oldest entry. OnRemoveWithMetadata func(key string, entry []byte, keyMetadata Metadata) // OnRemoveWithReason is a callback fired when the oldest entry is removed because of its expiration time or no space left // for the new entry, or because delete was called. A constant representing the reason will be passed through. // Default value is nil which means no callback and it prevents from unwrapping the oldest entry. // Ignored if OnRemove is specified. // 在缓存过期或者被删除时,可设置回调函数,参数是(key、val,reason)默认是nil不设置 OnRemoveWithReason func(key string, entry []byte, reason RemoveReason) onRemoveFilter int // Logger is a logging interface and used in combination with `Verbose` // Defaults to `DefaultLogger()` Logger Logger }
BigCache的实现是 一种索引和数据分离的多阶hash。
主索引(多阶hash数组)的value保存的是在数据段的位置,通过二次定位拿到某个key对应的真实的value。
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