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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.



  • 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.


  • 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.


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