groupcache: Index | Files | Directories

package groupcache

import ""

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.


Package Files

byteview.go groupcache.go http.go peers.go sinks.go

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.

func RegisterServerStart

func RegisterServerStart(fn func())

RegisterServerStart registers a hook that is run when the first group is created.

type AtomicInt

type AtomicInt int64

An AtomicInt is an int64 to be accessed atomically.

func (*AtomicInt) Add

func (i *AtomicInt) Add(n int64)

Add atomically adds n to i.

func (*AtomicInt) Get

func (i *AtomicInt) Get() int64

Get atomically gets the value of i.

func (*AtomicInt) String

func (i *AtomicInt) String() string

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) At

func (v ByteView) At(i int) byte

At returns the byte at index i.

func (ByteView) ByteSlice

func (v ByteView) ByteSlice() []byte

ByteSlice returns a copy of the data as a byte slice.

func (ByteView) Copy

func (v ByteView) Copy(dest []byte) int

Copy copies b into dest and returns the number of bytes copied.

func (ByteView) Equal

func (v ByteView) Equal(b2 ByteView) bool

Equal returns whether the bytes in b are the same as the bytes in b2.

func (ByteView) EqualBytes

func (v ByteView) EqualBytes(b2 []byte) bool

EqualBytes returns whether the bytes in b are the same as the bytes in b2.

func (ByteView) EqualString

func (v ByteView) EqualString(s string) bool

EqualString returns whether the bytes in b are the same as the bytes in s.

func (ByteView) Len

func (v ByteView) Len() int

Len returns the view's length.

func (ByteView) ReadAt

func (v ByteView) ReadAt(p []byte, off int64) (n int, err error)

ReadAt implements io.ReaderAt on the bytes in v.

func (ByteView) Reader

func (v ByteView) Reader() io.ReadSeeker

Reader returns an io.ReadSeeker for the bytes in v.

func (ByteView) Slice

func (v ByteView) Slice(from, to int) ByteView

Slice slices the view between the provided from and to indices.

func (ByteView) SliceFrom

func (v ByteView) SliceFrom(from int) ByteView

SliceFrom slices the view from the provided index until the end.

func (ByteView) String

func (v ByteView) String() string

String returns the data as a string, making a copy if necessary.

type CacheStats

type CacheStats struct {
    Bytes     int64
    Items     int64
    Gets      int64
    Hits      int64
    Evictions int64

CacheStats are returned by stats accessors on Group.

type CacheType

type CacheType int

CacheType represents a type of cache.

const (
    // The MainCache is the cache for items that this peer is the
    // owner for.
    MainCache CacheType = iota + 1

    // The HotCache is the cache for items that seem popular
    // enough to replicate to this node, even though it's not the
    // owner.

type Context

type Context interface{}

Context is an opaque value passed through calls to the ProtoGetter. It may be nil if your ProtoGetter implementation does not require a context.

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, key string, dest Sink) error

A Getter loads data for a key.

type GetterFunc

type GetterFunc func(ctx Context, key string, dest Sink) error

A GetterFunc implements Getter with a function.

func (GetterFunc) Get

func (f GetterFunc) Get(ctx Context, key string, dest Sink) error

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

func GetGroup(name string) *Group

GetGroup returns the named group previously created with NewGroup, or nil if there's no such group.

func NewGroup

func NewGroup(name string, cacheBytes int64, getter Getter) *Group

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.

func (*Group) Get

func (g *Group) Get(ctx Context, key string, dest Sink) error

func (*Group) Name

func (g *Group) Name() string

Name returns the name of the group.

type HTTPPool

type HTTPPool struct {
    // Context optionally specifies a context for the server to use when it
    // receives a request.
    // If nil, the server uses a nil Context.
    Context func(*http.Request) 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) http.RoundTripper
    // contains filtered or unexported fields

HTTPPool implements PeerPicker for a pool of HTTP peers.

func NewHTTPPool

func NewHTTPPool(self string) *HTTPPool

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 be a valid base URL that points to the current server, for example "".

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) PickPeer

func (p *HTTPPool) PickPeer(key string) (ProtoGetter, bool)

func (*HTTPPool) ServeHTTP

func (p *HTTPPool) ServeHTTP(w http.ResponseWriter, r *http.Request)

func (*HTTPPool) Set

func (p *HTTPPool) Set(peers ...string)

Set updates the pool's list of peers. Each peer value should be a valid base URL, for example "".

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.

func (NoPeers) PickPeer

func (NoPeers) PickPeer(key string) (peer ProtoGetter, ok bool)

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, 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

func AllocatingByteSliceSink(dst *[]byte) Sink

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

func ByteViewSink(dst *ByteView) Sink

ByteViewSink returns a Sink that populates a ByteView.

func ProtoSink

func ProtoSink(m proto.Message) Sink

ProtoSink returns a sink that unmarshals binary proto values into m.

func StringSink

func StringSink(sp *string) Sink

StringSink returns a Sink that populates the provided string pointer.

func TruncatingByteSliceSink

func TruncatingByteSliceSink(dst *[]byte) Sink

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.


consistenthashPackage consistenthash provides an implementation of a ring hash.
lruPackage lru implements an LRU cache.
singleflightPackage singleflight provides a duplicate function call suppression mechanism.

Package groupcache imports 16 packages (graph) and is imported by 26 packages. Updated 2016-05-16. Refresh now. Tools for package owners.