Common misunderstandings and answers to PHP development caching

Common misunderstandings and answers to caching in PHP development

With the continuous development of PHP technology, caching has become an indispensable part of PHP development. However, some common misunderstandings may arise due to differences in personal experience and knowledge levels. This article will introduce common misunderstandings about PHP development caching and provide corresponding answers. In addition, some specific code examples will be provided to help readers understand better.

Misunderstanding 1: Caching is meaningless, because PHP is already fast

Answer: Although PHP itself is fast, for some more complex applications, due to accessing the database Frequent operations such as working with external resources may cause the entire application to slow down. At this time, using cache can greatly improve the access speed of the application.

The following is a simple example:

First, we define a function get_data_from_db(), which is used to obtain data from the database:

function get_data_from_db($id) {
    // connect to database
    $db = new PDO('mysql:host=localhost;dbname=my_db;charset=utf8', 'username', 'password');
    // prepare statement
    $stmt = $db->prepare('SELECT * FROM my_table WHERE id = :id');
    $stmt->bindParam(':id', $id, PDO::PARAM_INT);
    // execute statement
    $stmt->execute();
    // fetch data
    $data = $stmt->fetch(PDO::FETCH_ASSOC);
    // close connection
    $db = null;
    // return data
    return $data;
}

Then, we define There is a function get_data(), which is used to obtain data from the cache:

function get_data($id) {
    // connect to cache server
    $cache = new Memcached();
    $cache->addServer('localhost', 11211);
    // get data from cache
    $data = $cache->get('my_key_' . $id);
    // if data is not in cache, get it from database and store it in cache
    if (!$data) {
        $data = get_data_from_db($id);
        $cache->set('my_key_' . $id, $data, 60); // cache data for 60 seconds
    }
    // return data
    return $data;
}

In this example, we use Memcached as the cache server. As you can see, we first try to get the data from the cache. If it is not obtained, we get the data from the database and then store it in the cache. In addition, we also set the cache expiration time to 60 seconds.

Through this example, it can be seen that using cache can greatly improve the access speed of the application, and it is also easy to implement. Therefore, caching is definitely not pointless.

Misunderstanding 2: Caching will cause data inconsistency

Answer: If the cache is used improperly, it will indeed lead to data inconsistency, but as long as it is used properly, this problem will not occur.

Here is an example:

Suppose we have a function get_data_from_db(), which is used to get data from the database, and the data is notified when it is updated:

function get_data_from_db($id) {
    // connect to database
    $db = new PDO('mysql:host=localhost;dbname=my_db;charset=utf8', 'username', 'password');
    // prepare statement
    $stmt = $db->prepare('SELECT * FROM my_table WHERE id = :id');
    $stmt->bindParam(':id', $id, PDO::PARAM_INT);
    // execute statement
    $stmt->execute();
    // fetch data
    $data = $stmt->fetch(PDO::FETCH_ASSOC);
    // close connection
    $db = null;
    // register notification handler
    $notifier = new MyDataNotifier();
    $notifier->register($id);
    // return data
    return $data;
}

Then, we define a function get_data(), which is used to get data from the cache, and will also send out notifications after the data is updated in the cache:

function get_data($id) {
    // connect to cache server
    $cache = new Memcached();
    $cache->addServer('localhost', 11211);
    // get data from cache
    $data = $cache->get('my_key_' . $id);
    // if data is not in cache, get it from database and store it in cache
    if (!$data) {
        $data = get_data_from_db($id);
        $cache->set('my_key_' . $id, $data);
    }
    // check if data is up-to-date
    $notifier = new MyDataNotifier();
    if ($notifier->is_up_to_date($id)) {
        // return data
        return $data;
    } else {
        // data is out of date, so get it from database and store it in cache
        $data = get_data_from_db($id);
        $cache->set('my_key_' . $id, $data);
        // return data
        return $data;
    }
}

In this example, we use a data Notification class MyDataNotifier, which is used to record the timestamp of data updates and can determine whether the data has expired.

As you can see, when the data is updated, we will send a notification in the get_data_from_db() function, and we will also check whether the data has expired in the get_data() function. If the data has expired, we will get new data from the database and update the data in the cache at the same time.

Through this example, we can see that as long as the cache is used properly, data inconsistency will not occur. This also shows that caching is not a panacea and needs to be used flexibly in combination with actual business scenarios.

Misunderstanding 3: Caching requires a lot of memory

Answer: Although using cache may consume a certain amount of memory, if used properly, it will not cause memory overhead as many people imagine. huge.

Here is an example:

Suppose we have a function get_data_from_db(), which is used to get data from the database, and the size of each data item is relatively large:

function get_data_from_db($id) {
    // connect to database
    $db = new PDO('mysql:host=localhost;dbname=my_db;charset=utf8', 'username', 'password');
    // prepare statement
    $stmt = $db->prepare('SELECT * FROM my_table WHERE id = :id');
    $stmt->bindParam(':id', $id, PDO::PARAM_INT);
    // execute statement
    $stmt->execute();
    // fetch data
    $data = $stmt->fetch(PDO::FETCH_ASSOC);
    // close connection
    $db = null;
    // return data
    return $data;
}

Then, we define a function get_data(), which is used to get data from the cache, and uses an LRU algorithm to limit the size of the cache:

function get_data($id) {
    // connect to cache server
    $cache = new Memcached();
    $cache->addServer('localhost', 11211);
    // get data from cache
    $data = $cache->get('my_key_' . $id);
    // if data is not in cache, get it from database and store it in cache
    if (!$data) {
        $data = get_data_from_db($id);
        $cache->set('my_key_' . $id, $data);
    }
    // check cache size and evict old data if necessary
    $stats = $cache->getStats();
    $max_bytes = 1024 * 1024; // maximum cache size is 1MB
    if ($stats['bytes'] > $max_bytes) {
        $cache->delete('oldest_key');
    }
    // return data
    return $data;
}

In this example, we use A Memcached instance manages the cache and uses an LRU algorithm to limit the cache size. Specifically, when we obtain cached data, we will also check the size of the cache. If the cache has reached the maximum limit, the oldest data item will be automatically deleted.

Through this example, you can see that when using cache, you can use some simple techniques to control the size of the cache to avoid the problem of excessive memory consumption.

Conclusion

Through the above examples, we can find that when we use cache when writing PHP applications, we need to pay attention to the following points:

• Cache is very Useful, it can greatly improve the access speed of the application;
• When using the cache, you need to pay attention to the consistency of the data to ensure that the data stored in the cache and the data in the database are synchronized;
• To avoid excessive memory consumption, you can control the size of the cache through some techniques, such as using the LRU algorithm.

Finally, I hope the above example can provide some reference for readers who use caching in PHP development.

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