SHMT (Static Hash Map Table)

SHMT is an implementation of a very fast key-value read-only hash map table for PHP7.

We have developed SHMT as a faster, dependency-free replacement for the PECL CHDB extension.

Features

SHMT

• is written in C.
• creates and uses its own memory-mapped binary file. This enable it to cache and share the loaded pages of the file across multiple processes.
• has an extremely fast initial load, regardless of the size of the binary file.
• internally implements a "perfect hash function" and guarantees O(1) lookup time in the worst cases.
• internally uses the very fast "MurmurHash3" hashing algorithm.
• doesn't require any external libraries.
• is PHP 7.x ready.

Limitations

• Supported maximum number of data array elements is 2^26 (67,108,864 on 32 bit systems) and 2^31 (2,147,483,648 on 64 bit systems).
• The data array keys and values are always cast to string.
• Data files cannot be exchanged between 32 bit and 64 bit systems or systems with different endianness.
• The code compiles and runs on Linux systems. Other platforms have not been tested.

PHP Class

public static boolean SHMT::create(string $filename, array $array)

• Creates a SHMT from the $array and writes it into the file $filename
• Returns true on success
• Throws exceptions on errors

public SHMT::__construct(string $filename)

• Constructs a new SHMT object and maps the SHMT file $filename into memory
• Throws exceptions on errors

public (string|null) SHMT::get(string $string)

• Attempts to find the value stored under the key $string
• Returns the value if the key $string exists, otherwise null

public array SHMT::keys()

• Returns the list of all keys stored in the SHMT.

Example

Create a SHMT:

$array = [
	'str_key' => 'test',
	123456789 => 12345
	-1 => ''
];

SHMT::create($filename = 'map.shmt', $array);

Read from a SHMT:

$shmt = new SHMT($filename);

echo $shmt->get('str_key');    // string(4) "test"
echo $shmt->get(123456789);    // string(5) "12345"
echo $shmt->get('123456789');  // string(5) "12345"
echo $shmt->get(-1);           // string(0) ""
echo $shmt->get('abc_xyz');    // NULL