Prepending in Memcached with Golang (Detailed Guide w/ Code Examples)

Use Case(s)

Prepending data is often used when you want to add information at the beginning of existing data in a cache. For instance, if you have a string value and later decide to include some metadata at the start of this string without disturbing the already stored value.

Code Examples

The gomemcache/memcache package provides the Prepend method for prepending data to an existing memcache item.

Here's an example:

package main

import (
	"log"
	"github.com/bradfitz/gomemcache/memcache"
)

func main() {
	mc := memcache.New("127.0.0.1:11211")

	err := mc.Set(&memcache.Item{Key: "foo", Value: []byte("world")})
	if err != nil {
		log.Fatal(err)
	}

	err = mc.Prepend("foo", []byte("Hello, "))
	if err != nil {
		log.Fatal(err)
	}

	it, err := mc.Get("foo")
	if err != nil {
		log.Fatal(err)
	}

	log.Println(string(it.Value)) // Prints: "Hello, world"
}

In this sample code, we set the value "world" for key "foo". Then we prepend "Hello, " to the existing value. Finally, we get the value for the key "foo" which now returns "Hello, world".

Best Practices

• Always check for errors after performing operations like Set or Prepend.
• Consider the maximum size limit for a value. As per Memcached protocol, the value should not exceed 1MB including the data being prepended.

Common Mistakes

• Not checking if the key already exists before prepending. The Prepend operation will fail if the key does not exist.
• Ignoring concurrency issues. Multiple clients can prepend data, which could result in unexpected order of data.

FAQs

Q: Can I prepend to non-string values? A: Yes, but be mindful that Memcached operates on byte arrays, so it's up to your application to interpret these bytes. If you're dealing with complex data types, consider serialization or a different method of composition.