How much memory does php array occupy?

In PHP, array is a very common data type and a very important data structure in data processing. When using arrays, people often focus on the performance and flexibility of arrays. However, many developers do not know the underlying implementation principles of arrays, nor do they know how much memory arrays occupy. This article will give readers a detailed introduction to the memory usage of PHP arrays.

First of all, we need to understand how arrays in PHP are implemented. According to the official PHP documentation, there are two underlying implementations of PHP arrays: hash tables and ordered arrays. A hash table is an array-based data structure, and the subscript of the array can be any integer or string. PHP array hash tables use hashing algorithms to quickly find or insert a key-value pair.

There is a zval structure implemented in C language at the bottom of the PHP array. This structure is similar to a variable container, used to store PHP variables. For PHP arrays, one zval corresponds to one array element. A hash table is implemented as an array of zval structure pointers. Specifically, each element of the array contains two zval structures, one to store the key and one to store the value. Therefore, the memory footprint of a PHP array includes the memory space for the keys and values, as well as the memory space for the array of pointers used to store the hash table.

So, how to calculate the memory usage of PHP array? We can use the following code to test the memory usage of a simple array:

$data = array(
    'key1' => 'value1',
    'key2' => 'value2',
    'key3' => 'value3'
);

echo memory_get_usage(true);

Running the above code will output an integer indicating the memory size currently used by the PHP script. If you call memory_get_usage() once before output, you can get the memory size consumed by the script execution itself. If you run the entire script and call memory_get_usage() again, you can get the memory size occupied by the PHP process. The difference between these two values ​​is the size of the memory space allocated to the array during the execution of this script.

For example, on my computer, the output value obtained by executing the above code is: 4096. This means that this simple array takes up 4096 bytes or 4 KB of memory space. However, it should be noted that this value also includes the memory space occupied by other PHP data types, such as strings, numbers, objects, etc., so this value is not completely accurate.

If we want to more accurately calculate the memory space occupied by PHP arrays, we can use PHP's built-in functions memory_get_usage() and serialize(). serialize() The function can serialize a PHP variable into a string. This string contains information such as variable name, data type and content. We can estimate the memory size occupied by a PHP array by subtracting the length of the original variable from the length of the serialized string.

The following is a sample code:

$data = array(
    'key1' => 'value1',
    'key2' => 'value2',
    'key3' => 'value3'
);

$size = strlen(serialize($data)) - strlen(var_export($data, true));

echo $size;

On my computer, running the above code can get an output value of 132. This means that this simple array takes up 132 bytes or 0.132 KB of memory space. This estimate is affected by many factors, such as the number of array elements, the length of the array keys and values, etc. But no matter what, this method can provide us with a relatively accurate memory usage.

Finally, it should be noted that the memory footprint of PHP arrays also depends on the PHP version and configuration. If you have an older version of PHP or use a lesser memory allocation strategy, the memory footprint may be larger. If you need to deal with large amounts of array data frequently, you can take some optimization measures, such as using the SPL data structure or converting the array keys to integer types when possible. This can effectively reduce the memory footprint of the array and improve the performance of PHP applications.

The above is the detailed content of How much memory does php array occupy?. For more information, please follow other related articles on the PHP Chinese website!