google/gomemcache

Go Memcached client library #golang

About

This is a memcache client library for the Go programming language (http://golang.org/).

It is a fork of https://github.com/bradfitz/gomemcache/memcache, with support for Autodiscovery client based on https://cloud.google.com/memorystore/docs/memcached/auto-discovery-overview

Installing

Using go get

$ go get github.com/google/gomemcache/memcache

After this command gomemcache is ready to use. Its source will be in:

$GOPATH/src/github.com/google/gomemcache/memcache

Example without Autodiscovery

import (
        "fmt"
        "github.com/google/gomemcache/memcache"
)

func main() {
     // Create a client by providing the list of memcached servers.
     mc := memcache.New("10.0.0.1:11211", "10.0.0.2:11211", "10.0.0.3:11212")

     // For data queries (e.g., SET/GET), the client will first select a
     // memcached server based on computed hash of the key and then send
     // the query to that server.
     mc.Set(&memcache.Item{Key: "foo", Value: []byte("my value")})

     it, _ := mc.Get("foo")
     fmt.Println(string(it.Value)) // Expecting "my value" to be printed
}

Example with Autodiscovery

import (
        "fmt"
        "time"
        "github.com/google/gomemcache/memcache"
)

func main() {
     // Create a client by providing the autodiscovery endpoint. Behind the
     // scene, the client queries the autodiscovery endpoint to fetch the
     // list of memcached servers.
     mcDiscovery, _ := memcache.NewDiscoveryClient("10.0.0.1:11211", 30 * time.Second)

     // For data queries (e.g., SET/GET), the client will first select a
     // memcached server based on computed hash of the key and then send
     // the query to that server.
     mcDiscovery.Set(&memcache.Item{Key: "foo", Value: []byte("my value")})

     it, _ := mcDiscovery.Get("foo")
     fmt.Println(string(it.Value)) // Expecting "my value" to be printed

     mcDiscovery.StopPolling()
}

Note

Remember to call StopPolling() on the discovery enabled client to stop the polling, else this can leak "go" methods.

Full docs, see:

See https://godoc.org/github.com/google/gomemcache/memcache

Or run:

$ godoc github.com/google/gomemcache/memcache

gomemcache's Issues

Prevent autodiscovery to go to old version if new version has been seen

Currently, autodiscovery can go to an older discovery information after it has already discovered new information.

To fix this, configID extracted on line:[1] should be checked with the last discovered config ID and clusterConfig.NodeAddresses should be updated only if clusterConfig.ConfigID < newConfigID

[1]

gomemcache/memcache/cluster_config_parser.go

Line 67 in 9428199

configID, parseError := strconv.ParseInt(configIDLine, 10, 64)

Misleading comment about thread safety?

In updateServerList there is this comment:

gomemcache/memcache/config_poller.go

Line 114 in c1c93e4

// updateServerList is not thread safe and should not be called without holding lock on clusterConfigMU

However, when the method is called here:

gomemcache/memcache/config_poller.go

Line 109 in c1c93e4

c.updateServerList(clusterConfig)

I don't see that it is called with any mutex held. I only see clusterConfigMU ever held with a read-lock.

However, I believe there isn't actually a thread safety concern here. The prevClusterConfig appears to only be read/updated from readConfigAndUpdateServerList which is never called concurrently in the current code. The SetServers call on the ServerList is protected by a mutex so that is already protected. From what I can tell, the clusterConfigMU lock and thread safety comments could likely be removed to avoid confusion.