memd

memd is a memcached useful client wrapping https://github.com/douban/libmc

memd focuses on transparent managing chain for multi layer memcached. The main methods are GetOrSet and GetOrSetMulti.

Installing

Using go get

$ go get github.com/mosasiru/memd

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

$GOPATH/src/github.com/mosasiru/memd

Example

GetOrSet

package main

import (
	"github.com/douban/libmc/golibmc"
	"github.com/mosasiru/memd"
	"log"
)

type Result struct {
	Hoge int    `json:"hoge"`
}

func main() {
	c := memd.New(golibmc.SimpleNew([]string{"localhost:11211"}))

	item, err := c.GetOrSet("key", func(key string) (*golibmc.Item, error) {
		return c.ToItem(key, getResultFromDB(key), 10)
	})
	if err != nil {
        return
	}
	res := Result{}
	if err := c.FromItem(item, &res); err != nil {
        return
	}
	log.Printf("%d", res.Hoge)
}

func getResultFromDB(key string) Result {
	return Result{1} // dummy
}

This is a simple example for GetOrSet.

GetOrSet is a useful method combining Get and Set.

GetOrSet works as Get from memcached first, and if no hit, Set value the callback returns (for example DB result), then return the value.

ToItem is a method for generating *golibmc.Item. It serialize a value with json as default.

FromItem is a method for deserializing *golibmc.Item. FromItem deserialize it with json as default.

GetOrSet for multi layer memcached

package main

import (
	"github.com/douban/libmc/golibmc"
	"github.com/mosasiru/memd"
	"log"
)

type Result struct {
	Hoge int    `json:"hoge"`
}

func main() {
	localMemd := memd.New(golibmc.SimpleNew([]string{"localhost:11211"}))
	remoteMemd := memd.New(golibmc.SimpleNew([]string{"remotehost:11211"}))

    item, err := localMemd.GetOrSet("key", func(key string) (*golibmc.Item, error) {
		return remoteMemd.GetOrSet(key, func(key string) (*golibmc.Item, error) {
			return remoteMemd.ToItem(key, getResultFromDB(key), 1)
		})
	})
	if err != nil {
        return
	}
	res := Result{}
	if err := localMemd.FromItem(item, &res); err != nil {
        return
	}
	log.Printf("%d", res.Hoge)
}

func getResultFromDB(key string) Result {
	return Result{1} // dummy
}

This is a GetOrSet example for multi layer memcached, specifically local memcached and remote memcached. GetOrSet can chain transparently.

GetOrSetMulti

Consider that we want cache a SQL query such that select * from hoge where id in (100,200,300...) for each id. In other words, another query could be select * from hoge where id in (100,400...). so we want to cache as per id, not as whole result. In such a case, we use GetMulti for ids first, and if no hit key exists, ask SQL for remain ids, then SetMulti DB values.

GetOrSetMulti makes easier such a situation. Below is the example.

package main

import (
	"github.com/douban/libmc/golibmc"
	"github.com/mosasiru/memd"
	"log"
)

type Result struct {
	Hoge int   `json:"hoge"`
}

func main() {
	c := memd.New(golibmc.SimpleNew([]string{"localhost:11211"}))
	keys := []string{"key1", "key2", "key3"}
	itemMap, err := c.GetOrSetMulti(keys, func(keys []string) (map[string]*golibmc.Item, error) {
		return c.ToItemMap(getResultMapFromDB(keys), 1)
	})
	if err != nil {
        return
	}
	for key, item := range itemMap {
		var res Result
		if err = c.FromItem(item, &res); err != nil {
            return
		}
		log.Printf("%s: %d", key, res.Hoge)
	}

}

func getResultMapFromDB(keys []string) map[string]interface{} {
	// dummy
	res := map[string]interface{}{}
	for _, key := range keys {
		res[key] = Result{1}
	}
	return res
}

GetOrSetMulti can chain as same as GetOrSet. Below code is an example.

itemMap, err := localMemd.GetOrSetMulti(keys, func(keys []string) (map[string]*golibmc.Item, error) {
    return remoteMemd.GetOrSetMulti(keys, func(keys []string) (map[string]*golibmc.Item, error) {
        return remoteMemd.ToItemMap(getResultMapFromDB(keys), 1)
    })
})

SetLogger

c := memd.New(golibmc.SimpleNew([]string{"localhost:11211"}))
c.SetLogger(log.Printf)

GetOrSet and GetOrSetMulti hit state is logged. the default logger is log.Printf. you can change that logger.

SetSerializer

ToItem, ToItemMap, and FromItem use json as a serializer. you can use other serializer with https://github.com/ugorji/go Handle. json, msgpack, binc, and so on.