Node.js Memcached Prepend Operations (Detailed Guide w/ Code Examples)

Use Case(s)

The prepend operation in Memcached is used to prepend data to an existing key's value. This is commonly used when you need to add information at the beginning of the current value stored against a key. For instance, it can be used for logging or tracking systems where most recent events need to be added at the start.

Code Examples

Let's suppose we have a Memcached instance running and we are using the memcached npm module in a Node.js application.

Example 1: Basic Prepend Operation

const memcached = require('memcached');
const client = new memcached('localhost:11211');

// set a key
client.set('key', 'world!', 10000, function(err) { /* handle error */ });

// prepend to a key
client.prepend('key', 'Hello ', function(err) {
  if(err) console.error(err);
  
  // get key
  client.get('key', function(err, data) {
    if(err) console.error(err);
    else console.log(data);  // -> 'Hello world!'
  });
});

In this example, we first set a key-value pair ('key': 'world!'). Then, we use the prepend method to prepend the string 'Hello ' to the current value of the key. Thus, the new value of the key becomes 'Hello world!'.

Best Practices

1. Error Handling: Always handle errors properly in your callbacks to prevent unexpected program behavior.
2. Key Existence: Remember that the prepend operation only works on keys that already exist in Memcached. Make sure the key exists before trying to prepend.

Common Mistakes

1. Assuming Key Creation: prepend operation doesn't create a new key if it doesn't exist already; it might lead to confusion because no error is thrown, but the operation doesn't have any effect either.
2. Concurrency Issues: If multiple clients are prepending to and reading from the same key simultaneously, race conditions may occur leading to unexpected results.

FAQs

Q: Can I prepend data to non-string values in Memcached?
A: No, Memcached only supports string values. Therefore, you can only prepend data to keys that hold string values.