As the documentation says, SplFixedArray is meant to be *faster* than array. Do not blindly believe other people's benchmarks, and beextra careful with the user comments on php.net. For instance, nairbv's benchmark code is completely wrong. Among other errors, it intends to increase the size of the arrays, but always initialize a 20 elements SplFixedArray.
On a PHP 5.4 64 bits linux server, I found SplFixedArray to be always faster than array().
* small data (1,000):
* write: SplFixedArray is 15 % faster
* read: SplFixedArray is 5 % faster
* larger data (512,000):
* write: SplFixedArray is 33 % faster
* read: SplFixedArray is 10 % faster
The SplFixedArray class
(PHP 5 >= 5.3.0, PHP 7, PHP 8)
Introduction
The SplFixedArray class provides the main functionalities of array. The main difference between a SplFixedArray and a normal PHP array is that the SplFixedArray must be resized manually and allows only integers within the range as indexes. The advantage is that it uses less memory than a standard array.
Class synopsis
/* Methods */
}Changelog
| Version | Description |
|---|---|
| 8.2.0 | The SplFixedArray::__serialize() and SplFixedArray::__unserialize() magic methods have been added to SplFixedArray. |
| 8.1.0 | SplFixedArray implements JsonSerializable now. |
| 8.0.0 | SplFixedArray implements IteratorAggregate now. Previously, Iterator was implemented instead. |
Examples
Example #1 SplFixedArray usage example
<?php
// Initialize the array with a fixed length
$array = new SplFixedArray(5);
$array[1] = 2;
$array[4] = "foo";
var_dump($array[0]); // NULL
var_dump($array[1]); // int(2)
var_dump($array["4"]); // string(3) "foo"
// Increase the size of the array to 10
$array->setSize(10);
$array[9] = "asdf";
// Shrink the array to a size of 2
$array->setSize(2);
// The following lines throw a RuntimeException: Index invalid or out of range
try {
var_dump($array["non-numeric"]);
} catch(RuntimeException $re) {
echo "RuntimeException: ".$re->getMessage()."\n";
}
try {
var_dump($array[-1]);
} catch(RuntimeException $re) {
echo "RuntimeException: ".$re->getMessage()."\n";
}
try {
var_dump($array[5]);
} catch(RuntimeException $re) {
echo "RuntimeException: ".$re->getMessage()."\n";
}
?>The above example will output:
NULL int(2) string(3) "foo" RuntimeException: Index invalid or out of range RuntimeException: Index invalid or out of range RuntimeException: Index invalid or out of range
Table of Contents
- SplFixedArray::__construct — Constructs a new fixed array
- SplFixedArray::count — Returns the size of the array
- SplFixedArray::current — Return current array entry
- SplFixedArray::fromArray — Import a PHP array in a SplFixedArray instance
- SplFixedArray::getIterator — Retrieve the iterator to go through the array
- SplFixedArray::getSize — Gets the size of the array
- SplFixedArray::jsonSerialize — Returns a representation that can be converted to JSON
- SplFixedArray::key — Return current array index
- SplFixedArray::next — Move to next entry
- SplFixedArray::offsetExists — Returns whether the requested index exists
- SplFixedArray::offsetGet — Returns the value at the specified index
- SplFixedArray::offsetSet — Sets a new value at a specified index
- SplFixedArray::offsetUnset — Unsets the value at the specified $index
- SplFixedArray::rewind — Rewind iterator back to the start
- SplFixedArray::__serialize — Serializes the SplFixedArray object
- SplFixedArray::setSize — Change the size of an array
- SplFixedArray::toArray — Returns a PHP array from the fixed array
- SplFixedArray::__unserialize — Deserializes the data parameter into an SplFixedArray object
- SplFixedArray::valid — Check whether the array contains more elements
- SplFixedArray::__wakeup — Reinitialises the array after being unserialised
add a note
User Contributed Notes 8 notes
artaxerxes ¶
12 years ago
herhor67 at interia dot pl ¶
4 years ago
Memory usage for arrays of 1132766 ints (data derived from some 1kx1k img):
Regular: 76453160B (67.5B/int)
SplFixed: 18898744B (16.7B/int)
In my application, SFA uses 75% less RAM, which is a life-saver.
Speed comparison:
Regular: 449ms
SplFixed (resized before every element): 791ms
SplFixed (fully preallocated): 392ms
SplFixed (preall-d to 1M and then resized): 547ms
Pros and cons:
+ much more efficient RAM-wise
+ a bit faster if max size is known
~ a bit slower if max size is only approximated
- much slower if max size is not known
- cannot be used with most array functions
To sum up:
SplFixedArray is a very good choice for storing giant amount of data, though only as long as you at least roughly know the size and can work without array functions.
chrisstocktonaz at gmail dot com ¶
15 years ago
Note, that this is considerably faster and should be used when the size of the array is known. Here are some very basic bench marks:
<?php
for($size = 1000; $size < 50000000; $size *= 2) {
echo PHP_EOL . "Testing size: $size" . PHP_EOL;
for($s = microtime(true), $container = Array(), $i = 0; $i < $size; $i++) $container[$i] = NULL;
echo "Array(): " . (microtime(true) - $s) . PHP_EOL;
for($s = microtime(true), $container = new SplFixedArray($size), $i = 0; $i < $size; $i++) $container[$i] = NULL;
echo "SplArray(): " . (microtime(true) - $s) . PHP_EOL;
}
?>
OUTPUT
Testing size: 1000
Array(): 0.00046396255493164
SplArray(): 0.00023293495178223
Testing size: 2000
Array(): 0.00057101249694824
SplArray(): 0.0003058910369873
Testing size: 4000
Array(): 0.0015869140625
SplArray(): 0.00086307525634766
Testing size: 8000
Array(): 0.0024251937866211
SplArray(): 0.00211501121521
Testing size: 16000
Array(): 0.0057680606842041
SplArray(): 0.0041120052337646
Testing size: 32000
Array(): 0.011334896087646
SplArray(): 0.007631778717041
Testing size: 64000
Array(): 0.021990060806274
SplArray(): 0.013560056686401
Testing size: 128000
Array(): 0.053267002105713
SplArray(): 0.030976057052612
Testing size: 256000
Array(): 0.10280108451843
SplArray(): 0.056283950805664
Testing size: 512000
Array(): 0.20657992362976
SplArray(): 0.11510300636292
Testing size: 1024000
Array(): 0.4138810634613
SplArray(): 0.21826505661011
Testing size: 2048000
Array(): 0.85640096664429
SplArray(): 0.46247816085815
Testing size: 4096000
Array(): 1.7242450714111
SplArray(): 0.95304894447327
Testing size: 8192000
Array(): 3.448086977005
SplArray(): 1.96746301651
alex dot andrienko at gmail dot com ¶
14 years ago
Memory footprint of splFixedArray is about 37% of a regular "array" of the same size.
I was hoping for more, but that's also significant, and that's where you should expect to see difference, not in "performance".
CK ¶
1 year ago
Be warned that SplFixedArray does not provide all of the main functionalities of array. For example, it does not support array_slice. SplFixedArray should be far more efficient at supporting such array operations than normal arrays (since it should be simply a contiguous slice). Check that all your main array functions are really supported before trying to use SplFixedArray instead of array. With JIT in PHP8, some loops to polyfill these are perhaps now realistic, but still not as fast as native functions.
Anonymous ¶
7 years ago
PHP Arrays are very fast, and faster overall, especially in PHP7. You almost never need this. There are some cases where using this is better than using arrays but beware that they aren't that obvious.
php at stij dot nospam dot npeete dot nospam dot rs dot nl ¶
6 years ago
Note that (as of PHP 7.1) SplFixedArray uses 16 bytes (!) per array item. This can be checked easily via:
<?php
ini_set('memory_limit', '4M');
$array = new SplFixedArray(1000000);
//PHP Fatal error: Allowed memory size of 4194304 bytes exhausted (tried to allocate 16000000 bytes)
?>
So if you're considering SplFixedArray because you need to use large arrays with very large numbers of items, make sure you have enough memory to support them.
