Java Memcached Set Operations (Detailed Guide w/ Code Examples)

Use Case(s)

"Java Memcached Set" is a common operation used when working with Memcached in the context of a Java application. This operation is used to add or update a key-value pair in the cache. A few common use cases are:

  • Rapid retrieval of previously expensive computations or database queries.
  • Keeping track of session information across multiple servers in a load-balanced environment.
  • Storing user preferences or other frequently accessed but rarely updated data.

Code Examples

Here's an example of how to use the set operation using the xmemcached client:

import net.rubyeye.xmemcached.MemcachedClient; import net.rubyeye.xmemcached.XMemcachedClientBuilder; XMemcachedClientBuilder builder = new XMemcachedClientBuilder(AddrUtil.getAddresses("localhost:11211")); MemcachedClient memcachedClient =; String key = "user:1"; String value = "John Doe"; // Set the key-value pair in Memcached memcachedClient.set(key, 0, value);

In this code, we're creating a connection to a Memcached server running on localhost at port 11211. Then we're using the set method to store a string value associated with a key in Memcached.

Best Practices

  • Always handle potential exceptions that could be thrown by your Memcached client. These could occur due to connection issues, timeouts, or serialization problems.
  • Be aware of the size limits of keys and values - the maximum key length is 250 bytes, and the maximum size of a value is 1MB.
  • Make sure to close the MemcachedClient when you're done with it to free up resources.

Common Mistakes

  • Using complex Java objects as keys can lead to unexpected behavior, as these need to be serialized and deserialized. It's generally best to stick with simple types like strings or integers for keys.
  • Not understanding how Memcached's LRU (Least Recently Used) eviction strategy works. When Memcached runs out of memory, it will start evicting the least recently used items, regardless of their expiration time.


Q: What happens if I set a key that already exists in Memcached?
A: The old value will be overwritten by the new value. If you want to avoid overwriting existing values, consider using the add operation instead.

Q: Can I use Java objects as values when setting keys in Memcached?
A: Yes, you can store any Serializable object as a value. However, you should be aware of the serialization and deserialization overhead for large or complex objects.

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