Memcached - A Distributed Memory Object Caching System

Here's an overview of memcached: what it is, why it's valuable, and more!

Siva Prasad Rao Janapati

Mar. 30, 16 · Analysis

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In this article, we will learn about Memcached. Let us see what it is? How can we use it?

What is “Memcached”?

Memcached is an in-memory key-value store for small chunks of arbitrary data (strings, objects) from results of database calls, API calls, or page rendering HTML . Memcached uses LRU caching algorithm(Least Recently Used (LRU) – discards the least recently used items first).

Why “Memcached”?

It's free and source
To achieve high performance
It's Simple to set up
Ease of development
Client APIs are available for most of the popular languages

Who is Using “Memcached”?

Youtube.com
Digg.com
Twitter.com
Wikipedia.com
Flickr
Craiglist.com
and the list goes on ...........

Why Do We Need to Use “Memcached”?

To achieve high performance
To achieve high scalability

The architecture of the traditional system is given below.

Traditional Web Architecture

In the above design, the cache is part of the application server's JVM. In this case, some of the memory is allocated for the cache from the heap size allotted to the JVM. If the cache size increases, then the heap size need to increase. There is no better control over the cache because the cache is tightly associated with the app server's JVM. To have better control, we need to separate the cache from the app server's JVM.

High Scalability Architecture

In the above design, we have separated the cache from the application's JVM. This gives better control to manage the cache in a separate server. Based on the data size to cache, we can increase the cache server capacity without affecting the application.

How to Install and Set Up “Memcached”?

I have used Ubuntu operating system to install and set up the memcacahed. Follow the below steps to install and run the memcahed.

Download the source code from https://memcached.org/files/memcached-1.4.25.tar.gz
Extract the downloaded file and get into the extracted folder.
Run the below commands
- ./configure
- Make & make install
After successful installation, start the memcached using memcached -u <user name>
The Memcached server will run by default on 11211 port
Now, open a new command prompt and try to connect to the Memcached through telnet . For example telnet <host> 11211. If you are able to connect successfully to the Memcached server then the you are done with the installation and the setup.

What Operations Can We Perform With “Memcached”?

After establishing the connection to the memcached through telnet, we can perform the below operations.

Operation	Format	Parameters	Return Value
Set (Store key/value pair in Memcached)	set <key> <flags> <exptime> <bytes>	<key> : the key of the data stored <flags> : 32-bit unsigned integer that the server store with the data (provided by the user), and return along the data when the item is retrieved <exptime> : expiration time in seconds, 0 mean no delay, if exptime is superior to 30 days, Memcached will use it as a UNIX time stamps for expiration <bytes> : number of bytes in the data block	STORED to indicate success NOT_STORED indicate that the data was not stored because condition for “add” or “replace” command wasn’t met, or the item is in a delete queue
Get (Get value for key)	get <key>	<key> : the key of the data stored. To retrieve client can request value of multiple keys separated by white space	VALUE <flag> <bytes>\r\n<data> END indicate the end of response
Add (Store key/value pair in Memcached, but only if the server doesn’t already hold data for this key)	add <key> <flags> <exptime> <bytes>	<key> : the key of the data stored <flags> : 32-bit unsigned integer that the server store with the data (provided by the user), and return along the data when the item is retrieved <exptime> : expiration time in seconds, 0 mean no delay, if exptime is superior to 30 days, Memcached will use it as a UNIX time stamps for expiration <bytes> : number of bytes in the data block	STORED to indicate success NOT_STORED indicate that the data was not stored because condition for “add” or “replace” command wasn’t met, or the item is in a delete queue
Replace (Store key/value pair in Memcached, but only if the server already hold data for this key)	replace <key> <flags> <exptime><bytes>
Delete (Deletes key/value pair in Memcached)	delete <key>
Flush_all (Flush the server key/value pair (invalidating them) )	flush_all
stats (Return general-purpose statistics like up time, version, memory occupation, …)	stats
Item stats (Return items statistics, will display items statistics (count, age, eviction, …))	stats items

How to Use JAVA Client API?

Follow the below steps to use the JAVA client API.

To contact Memcached from Java, download the java client from http://code.google.com/p/spymemcached/
Get Memcached client

MemcachedClient client = new MemcachedClient(new InetSocketAddress(“localhost”, 11211));

After the completion of operations, call shutdown() on memcached client.

Memcached Cache (computing) operating system Data (computing) Memory (storage engine) Object (computer science) Java (programming language)

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