How to implement Memcached database sharding in PHP

With the development of web applications, the complexity of data processing is getting higher and higher. To provide better scalability and performance, many applications have adopted NoSQL databases. Memcached is a popular NoSQL in-memory cache that can significantly improve the response time of web applications while providing high availability of data.

However, as the application grows, the storage capacity of a single instance of Memcached may reach its limit. In this case, Memcached database sharding technology needs to be used to spread the data across multiple servers. In this article, we will learn how to implement Memcached database sharding using PHP.

Memcached server sharding

In Memcached, a hash function is used to map the key of the data to a specific server. The hash function can be MD5, CRC32, etc. When data is added or updated, Memcached uses a hash function to calculate the keys and determine which server to use. When using Memcached database sharding, we need to map keys to specific servers using the same method as a hash function. This can be done by following the steps:

1. Define server list
   In Memcached sharding, data needs to be stored in multiple servers. We can define an array that contains the IP address and port number of the server. For example:

$servers = array(

'192.168.1.101:11211', // Server 1
'192.168.1.102:11211', // Server 2
'192.168.1.103:11211' // Server 3

);

2. Calculate hash value
   In order to hash the data, you need to use A hash function. Memcached provides several built-in hash functions, including MD5 and CRC32. We can use any of them to calculate the hash value. For example, use the MD5 hash function:

$hash = md5('mykey');

3. Select server
   The hash value calculated using the hash function should Maps to the actual Memcached server. This can be done by dividing the hash value into intervals. For example, if there are three servers, we map the hashes to the ranges 0-32, 33-64, and 65-96. This can be done with the following steps:

• Calculate the hash of a 32-bit unsigned integer
• Divide the integer into intervals
• Map the intervals To the server

Use the following code to implement:

$hash = md5('mykey');
$hash_number = intval("0x".substr($hash, 0, 8));
$server_index = $hash_number % count($servers);
$server = $servers[$server_index];

In this example, we first use MD5 hash Hash maps "mykey" to a hash value. We then calculate the 32-bit unsigned integer value and calculate the modulus of that value using the length of the server array. This will give us a server index and we can use that index to get the correct server IP address and port number from the server list.

4. Storing Data
   In this step, we store the data on the Memcached server. In the case of using a server list, we need to use the Memcached classes from the Memcached extension library and pass the server list to them. At the same time, we also need to use the hash value and server from the previous step to determine the actual server where the data is stored. For example:

$memcached = new Memcached();
$memcached->addServers($servers);

$hash = md5('mykey');
$hash_number = intval("0x".substr($hash, 0, 8));
$server_index = $hash_number % count($servers);
$server = $servers[$server_index];

$memcached->setByKey($server, 'mykey', 'data', 60);

In this example, we first call addServers() of the Memcached class using the server array Method that specifies a list of servers to use. We then use the hash and server to call the setByKey() method to store the data into the correct server. We also provide an expiration time (60 seconds).

5. Get data
   When using sharding, you need to use the getByKey() method to retrieve data from the correct server. For example:

$hash = md5('mykey');
$hash_number = intval("0x".substr($hash, 0, 8));
$server_index = $hash_number % count($servers);
$server = $servers[$server_index];

$data = $memcached->getByKey($server, 'mykey');

In this example, we use the hash value and the server to call the getByKey() method to retrieve the data from the correct server. If the key does not exist, returns null.

Summary

When using Memcached, you can use sharding technology to store data on multiple servers. Using PHP, we can use the Memcached class in the Memcached extension library, which provides various methods for adding servers, setting up and getting data. Using a hash function, we can calculate the hash of the key and map it to the correct server. Remember, the choice of hash function and interval allocation will directly affect the balance and performance of the data.

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