Documentation ¶
Overview ¶
Package groupcache provides a data loading mechanism with caching and de-duplication that works across a set of peer processes.
Each data Get first consults its local cache, otherwise delegates to the requested key's canonical owner, which then checks its cache or finally gets the data. In the common case, many concurrent cache misses across a set of peers for the same key result in just one cache fill.
Index ¶
- Variables
- func RegisterNewGroupHook(fn func(*Group))
- func RegisterPeerPicker(fn func() PeerPicker)
- func RegisterPerGroupPeerPicker(fn func(groupName string) PeerPicker)
- func RegisterServerStart(fn func())
- type AtomicInt
- type ByteView
- func (v ByteView) At(i int) byte
- func (v ByteView) ByteSlice() []byte
- func (v ByteView) Copy(dest []byte) int
- func (v ByteView) Equal(b2 ByteView) bool
- func (v ByteView) EqualBytes(b2 []byte) bool
- func (v ByteView) EqualString(s string) bool
- func (v ByteView) Len() int
- func (v ByteView) ReadAt(p []byte, off int64) (n int, err error)
- func (v ByteView) Reader() io.ReadSeeker
- func (v ByteView) Slice(from, to int) ByteView
- func (v ByteView) SliceFrom(from int) ByteView
- func (v ByteView) String() string
- func (v ByteView) WriteTo(w io.Writer) (n int64, err error)
- type CacheStats
- type CacheType
- type Getter
- type GetterFunc
- type Group
- type HTTPPool
- type HTTPPoolOptions
- type NoPeers
- type PeerPicker
- type ProtoGetter
- type Sink
- type Stats
Constants ¶
This section is empty.
Variables ¶
var ( MGets = stats.Int64("gets", "The number of Get requests", unitDimensionless) MCacheHits = stats.Int64("cache_hits", "The number of times that either cache was good", unitDimensionless) MCacheMisses = stats.Int64("cache_misses", "The number of times that either cache was not good", unitDimensionless) MPeerLoads = stats.Int64("peer_loads", "The number of remote loads or remote cache hits", unitDimensionless) MPeerErrors = stats.Int64("peer_errors", "The number of remote errors", unitDimensionless) MLoads = stats.Int64("loads", "The number of gets/cacheHits", unitDimensionless) MLoadErrors = stats.Int64("loads_errors", "The number of errors encountered during Get", unitDimensionless) MLoadsDeduped = stats.Int64("loads_deduped", "The number of loads after singleflight", unitDimensionless) MLocalLoads = stats.Int64("local_loads", "The number of good local loads", unitDimensionless) MLocalLoadErrors = stats.Int64("local_load_errors", "The number of bad local loads", unitDimensionless) MServerRequests = stats.Int64("server_requests", "The number of Gets that came over the network from peers", unitDimensionless) MKeyLength = stats.Int64("key_length", "The length of keys", unitBytes) MValueLength = stats.Int64("value_length", "The length of values", unitBytes) MRoundtripLatencyMilliseconds = stats.Float64("roundtrip_latency", "Roundtrip latency in milliseconds", unitMillisecond) )
var AllViews = []*view.View{ {Name: "groupcache/gets", Description: "The number of Get requests", Measure: MGets, Aggregation: view.Count()}, {Name: "groupcache/cache_hits", Description: "The number of times that either cache was good", Measure: MCacheHits, Aggregation: view.Count()}, {Name: "groupcache/cache_misses", Description: "The number of times that either cache was not good", Measure: MCacheMisses, Aggregation: view.Count()}, {Name: "groupcache/peer_loads", Description: "The number of remote loads or remote cache hits", Measure: MPeerLoads, Aggregation: view.Count()}, {Name: "groupcache/peer_errors", Description: "The number of remote errors", Measure: MPeerErrors, Aggregation: view.Count()}, {Name: "groupcache/loads", Description: "The number of loads after singleflight", Measure: MLoads, Aggregation: view.Count()}, {Name: "groupcache/loads_deduped", Description: "The number of loads after singleflight", Measure: MLoadsDeduped, Aggregation: view.Count()}, {Name: "groupcache/local_loads", Description: "The number of good local loads", Measure: MLocalLoads, Aggregation: view.Count()}, {Name: "groupcache/local_load_errors", Description: "The number of bad local loads", Measure: MLocalLoadErrors, Aggregation: view.Count()}, {Name: "groupcache/server_requests", Description: "The number of Gets that came over the network from peers", Measure: MServerRequests, Aggregation: view.Count()}, {Name: "groupcache/key_length", Description: "The distribution of the key lengths", Measure: MKeyLength, Aggregation: defaultBytesDistribution}, {Name: "groupcache/value_length", Description: "The distribution of the value lengths", Measure: MValueLength, Aggregation: defaultBytesDistribution}, {Name: "groupcache/roundtrip_latency", Description: "The roundtrip latency", Measure: MRoundtripLatencyMilliseconds, Aggregation: defaultMillisecondsDistribution}, }
Functions ¶
func RegisterNewGroupHook ¶
func RegisterNewGroupHook(fn func(*Group))
RegisterNewGroupHook registers a hook that is run each time a group is created.
func RegisterPeerPicker ¶
func RegisterPeerPicker(fn func() PeerPicker)
RegisterPeerPicker registers the peer initialization function. It is called once, when the first group is created. Either RegisterPeerPicker or RegisterPerGroupPeerPicker should be called exactly once, but not both.
func RegisterPerGroupPeerPicker ¶
func RegisterPerGroupPeerPicker(fn func(groupName string) PeerPicker)
RegisterPerGroupPeerPicker registers the peer initialization function, which takes the groupName, to be used in choosing a PeerPicker. It is called once, when the first group is created. Either RegisterPeerPicker or RegisterPerGroupPeerPicker should be called exactly once, but not both.
func RegisterServerStart ¶
func RegisterServerStart(fn func())
RegisterServerStart registers a hook that is run when the first group is created.
Types ¶
type ByteView ¶
type ByteView struct {
// contains filtered or unexported fields
}
A ByteView holds an immutable view of bytes. Internally it wraps either a []byte or a string, but that detail is invisible to callers.
A ByteView is meant to be used as a value type, not a pointer (like a time.Time).
func (ByteView) EqualBytes ¶
EqualBytes returns whether the bytes in b are the same as the bytes in b2.
func (ByteView) EqualString ¶
EqualString returns whether the bytes in b are the same as the bytes in s.
func (ByteView) Reader ¶
func (v ByteView) Reader() io.ReadSeeker
Reader returns an io.ReadSeeker for the bytes in v.
type CacheStats ¶
CacheStats are returned by stats accessors on Group.
type Getter ¶
type Getter interface { // Get returns the value identified by key, populating dest. // // The returned data must be unversioned. That is, key must // uniquely describe the loaded data, without an implicit // current time, and without relying on cache expiration // mechanisms. Get(ctx context.Context, key string, dest Sink) error }
A Getter loads data for a key.
type GetterFunc ¶
A GetterFunc implements Getter with a function.
type Group ¶
type Group struct { // Stats are statistics on the group. Stats Stats // contains filtered or unexported fields }
A Group is a cache namespace and associated data loaded spread over a group of 1 or more machines.
func GetGroup ¶
GetGroup returns the named group previously created with NewGroup, or nil if there's no such group.
func NewGroup ¶
NewGroup creates a coordinated group-aware Getter from a Getter.
The returned Getter tries (but does not guarantee) to run only one Get call at once for a given key across an entire set of peer processes. Concurrent callers both in the local process and in other processes receive copies of the answer once the original Get completes.
The group name must be unique for each getter.
func (*Group) CacheStats ¶
func (g *Group) CacheStats(which CacheType) CacheStats
CacheStats returns stats about the provided cache within the group.
type HTTPPool ¶
type HTTPPool struct { // context.Context optionally specifies a context for the server to use when it // receives a request. // If nil, the server uses a nil context.Context. Context func(*http.Request) context.Context // Transport optionally specifies an http.RoundTripper for the client // to use when it makes a request. // If nil, the client uses http.DefaultTransport. Transport func(context.Context) http.RoundTripper // contains filtered or unexported fields }
HTTPPool implements PeerPicker for a pool of HTTP peers.
func NewHTTPPool ¶
NewHTTPPool initializes an HTTP pool of peers, and registers itself as a PeerPicker. For convenience, it also registers itself as an http.Handler with http.DefaultServeMux. The self argument should be a valid base URL that points to the current server, for example "http://example.net:8000".
func NewHTTPPoolOpts ¶
func NewHTTPPoolOpts(self string, o *HTTPPoolOptions) *HTTPPool
NewHTTPPoolOpts initializes an HTTP pool of peers with the given options. Unlike NewHTTPPool, this function does not register the created pool as an HTTP handler. The returned *HTTPPool implements http.Handler and must be registered using http.Handle.
func (*HTTPPool) Set ¶
Set updates the pool's list of peers. Each peer value should be a valid base URL, for example "http://example.net:8000".
type HTTPPoolOptions ¶
type HTTPPoolOptions struct { // BasePath specifies the HTTP path that will serve groupcache requests. // If blank, it defaults to "/_groupcache/". BasePath string // Replicas specifies the number of key replicas on the consistent hash. // If blank, it defaults to 50. Replicas int // HashFn specifies the hash function of the consistent hash. // If blank, it defaults to crc32.ChecksumIEEE. HashFn consistenthash.Hash }
HTTPPoolOptions are the configurations of a HTTPPool.
type NoPeers ¶
type NoPeers struct{}
NoPeers is an implementation of PeerPicker that never finds a peer.
type PeerPicker ¶
type PeerPicker interface { // PickPeer returns the peer that owns the specific key // and true to indicate that a remote peer was nominated. // It returns nil, false if the key owner is the current peer. PickPeer(key string) (peer ProtoGetter, ok bool) }
PeerPicker is the interface that must be implemented to locate the peer that owns a specific key.
type ProtoGetter ¶
type ProtoGetter interface {
Get(context context.Context, in *pb.GetRequest, out *pb.GetResponse) error
}
ProtoGetter is the interface that must be implemented by a peer.
type Sink ¶
type Sink interface { // SetString sets the value to s. SetString(s string) error // SetBytes sets the value to the contents of v. // The caller retains ownership of v. SetBytes(v []byte) error // SetProto sets the value to the encoded version of m. // The caller retains ownership of m. SetProto(m proto.Message) error // contains filtered or unexported methods }
A Sink receives data from a Get call.
Implementation of Getter must call exactly one of the Set methods on success.
func AllocatingByteSliceSink ¶
AllocatingByteSliceSink returns a Sink that allocates a byte slice to hold the received value and assigns it to *dst. The memory is not retained by groupcache.
func ByteViewSink ¶
ByteViewSink returns a Sink that populates a ByteView.
func StringSink ¶
StringSink returns a Sink that populates the provided string pointer.
func TruncatingByteSliceSink ¶
TruncatingByteSliceSink returns a Sink that writes up to len(*dst) bytes to *dst. If more bytes are available, they're silently truncated. If fewer bytes are available than len(*dst), *dst is shrunk to fit the number of bytes available.
type Stats ¶
type Stats struct { Gets AtomicInt // any Get request, including from peers CacheHits AtomicInt // either cache was good PeerLoads AtomicInt // either remote load or remote cache hit (not an error) PeerErrors AtomicInt Loads AtomicInt // (gets - cacheHits) LoadsDeduped AtomicInt // after singleflight LocalLoads AtomicInt // total good local loads LocalLoadErrs AtomicInt // total bad local loads ServerRequests AtomicInt // gets that came over the network from peers }
Stats are per-group statistics.
Source Files ¶
Directories ¶
Path | Synopsis |
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Package consistenthash provides an implementation of a ring hash.
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Package consistenthash provides an implementation of a ring hash. |
Package lru implements an LRU cache.
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Package lru implements an LRU cache. |
Package singleflight provides a duplicate function call suppression mechanism.
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Package singleflight provides a duplicate function call suppression mechanism. |