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Memcached key length limit – Top factors to consider

Looking for factors affecting the Memcached key length limit? Let’s have a closer look.

The maximum length of the key in Memcached has a restriction of 250 bytes.

At Bobcares, we get many queries on Memcached key limits, as a part of our Server Management Services.

Today, our Support Engineers will discuss major limits on Memcached keys.


A quick look on Memcached

Memcached is an open-source memory caching system. We use it to speed up dynamic web applications by reducing the database load. That is Memcached loads data from the cache to speed up websites.

The Memcached server is a big hash table suitable for websites with high database load. A hash table is a collection that stores key-value items.

One way to connect to the Memcached server is by using the telnet command. And the command usage is,

telnet <HOST> <PORT>

This connects the server to the Memcached server where we can store and retrieve data.

In Memcached, we can store a key and its corresponding value. We can also provide other details like the expiration time of the key, number of values, and a flag. But Memcached has some limitations on keys and values.

Our Support Engineers will provide a quick guide on them.


Limits on a Memcached key

Users use Memcached to store different keys and values. The major restriction in Memcached are:


1. Key length limit

The maximum length of the key string must be 250 bytes. And Memcached will not accept a key length more than that.

But for a customer storing URL as the key and string with a relevant keyword as the value, the size of the key is a limitation. Because URLs can have a length of more than 250 bytes.

Here increasing the value of the parameter KEY_MAX_LENGTH in the source code will not increase the limit.


2. Syntax restrictions

Similarly, the key name has some character restrictions. That is whitespaces and control characters in the key name throws an error in a line format.

The error appeared due to whitespace in the key name is,

Memcached key length limit.


3. Key expiration time

Another major limitation of the Memcached key is its expiration time. The maximum expiration time for a key is 30 days nevertheless it is set to zero.

That is the key will be automatically expired after the expiration time. So it will not be available afterward.

The expiration time also has another side, that is, the key will be expired only after the expiration time. So when a user updates the website, the older keys persist. To avoid that, the user should manually remove the keys.


4. Size of the value

In Memcached, there is a size limit for the item. The default value is 1 MB. To change this, we can edit the /etc/init.d/memcached file and add the parameter as


If a user adds a key without considering the limits, it ends up in the error ‘CLIENT_ERROR bad command line format’.


[Still, have any queries on Memcached keys? – We can help you.]



In short, the Memcached key length limit is 250 bytes. The key name in the Memcached has other limitations in size, syntax, expiration time, etc. Today, our Support Engineers provided some essentials details on this.


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