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


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.

Was this content helpful?

Start building today

Dragonfly is fully compatible with the Redis ecosystem and requires no code changes to implement.