PHP benchmark: String concatenation vs. Array join()

perf-test.php

<?php

function str_concat($size)
{
    $result = "";
    for ($i = 0; $i < $size; $i++) {
        $result .= (string)rand() . "\n";
    }
    return $result;
}

function array_join($size)
{
    $result = [];
    for ($i = 0; $i < $size; $i++) {
        $result [] = (string)rand() . "\n";
    }
    return join('', $result);
}

function array_join2($size)
{
    $result = [];
    for ($i = 0; $i < $size; $i++) {
        $result [] = (string)rand();
    }
    return join("\n", $result);
}

function test($size, $iterations)
{
    // run tests
    $t = microtime(true);
    for ($j = 0; $j < $iterations; $j++) {
        $x = str_concat($size);
    }
    $t1 = microtime(true) - $t;

    $t = microtime(true);
    for ($j = 0; $j < $iterations; $j++) {
        $x = array_join($size);
    }
    $t2 = microtime(true) - $t;

    $t = microtime(true);
    for ($j = 0; $j < $iterations; $j++) {
        $x = array_join2($size);
    }
    $t3 = microtime(true) - $t;

    // echo results as CSV
    printf("%s, %d, %d, %f, %f, %f\n", phpversion(), $size, $iterations, $t1, $t2, $t3);
}

echo "# PHP Version, Array Size, Iterations, str_concat, array_join, array_join2\n";
for ($i = 1; $i <= 100000; $i = $i * 10) {
    test($i, 1000);
}

perf-test.sh

#!/bin/bash

for ver in 5.6 7.0 7.1 7.2 7.3; do
  echo "# running tests for version $ver"

  image=php:$ver-cli
  docker run --rm -v "$PWD":/src $image \
    bash -c "php /src/perf-test.php"
done

results.txt

# running tests for version 5.6
# PHP Version, Parts Count, Iterations, str_concat, array_join, array_join2, array_join3, array_join4
5.6.40, 1, 1000, 0.001597, 0.001300, 0.001112, 0.001087, 0.001468
5.6.40, 10, 1000, 0.005058, 0.007327, 0.006817, 0.008745, 0.010718
5.6.40, 100, 1000, 0.057380, 0.061603, 0.070954, 0.058866, 0.086805
5.6.40, 1000, 1000, 0.515179, 0.626859, 0.657277, 0.809347, 1.323092
5.6.40, 10000, 1000, 5.058190, 7.374991, 7.665942, 6.673272, 11.688725
5.6.40, 100000, 1000, 52.133853, 71.907317, 76.902235, 67.298046, 111.846944
# running tests for version 7.0
# PHP Version, Parts Count, Iterations, str_concat, array_join, array_join2, array_join3, array_join4
7.0.33, 1, 1000, 0.000739, 0.000957, 0.000787, 0.000645, 0.000744
7.0.33, 10, 1000, 0.003980, 0.003915, 0.006549, 0.003564, 0.004391
7.0.33, 100, 1000, 0.061051, 0.033678, 0.037254, 0.029608, 0.044159
7.0.33, 1000, 1000, 0.336042, 0.332554, 0.373780, 0.291184, 0.342935
7.0.33, 10000, 1000, 3.231953, 3.307821, 3.915566, 2.909325, 4.061225
7.0.33, 100000, 1000, 31.976340, 35.209253, 43.898724, 30.411636, 37.618492
# running tests for version 7.1
# PHP Version, Parts Count, Iterations, str_concat, array_join, array_join2, array_join3, array_join4
7.1.32, 1, 1000, 0.000717, 0.000851, 0.000796, 0.000810, 0.000885
7.1.32, 10, 1000, 0.004571, 0.005157, 0.005320, 0.004284, 0.005708
7.1.32, 100, 1000, 0.046951, 0.043843, 0.042463, 0.032842, 0.033185
7.1.32, 1000, 1000, 0.316417, 0.314221, 0.382685, 0.271413, 0.330734
7.1.32, 10000, 1000, 3.605251, 2.855439, 3.496263, 2.446178, 3.149273
7.1.32, 100000, 1000, 28.017887, 30.284794, 38.747616, 26.073231, 32.535485
# running tests for version 7.2
# PHP Version, Parts Count, Iterations, str_concat, array_join, array_join2, array_join3, array_join4
7.2.23, 1, 1000, 0.000788, 0.000700, 0.001279, 0.000593, 0.000684
7.2.23, 10, 1000, 0.003656, 0.003471, 0.004541, 0.003646, 0.004430
7.2.23, 100, 1000, 0.044852, 0.027060, 0.035542, 0.023614, 0.030209
7.2.23, 1000, 1000, 0.274020, 0.297881, 0.327138, 0.237992, 0.282198
7.2.23, 10000, 1000, 2.742886, 2.812583, 3.303890, 2.627340, 3.123135
7.2.23, 100000, 1000, 27.193778, 31.518518, 40.634590, 27.752904, 37.442942
# running tests for version 7.3
# PHP Version, Parts Count, Iterations, str_concat, array_join, array_join2, array_join3, array_join4
7.3.10, 1, 1000, 0.000495, 0.000600, 0.000685, 0.000576, 0.000687
7.3.10, 10, 1000, 0.003745, 0.003689, 0.006031, 0.003448, 0.004353
7.3.10, 100, 1000, 0.046929, 0.030393, 0.027951, 0.024449, 0.030039
7.3.10, 1000, 1000, 0.290486, 0.279173, 0.323931, 0.244155, 0.319280
7.3.10, 10000, 1000, 2.696267, 2.776577, 3.294820, 2.355970, 3.226814
7.3.10, 100000, 1000, 26.631122, 30.527062, 42.366897, 27.234378, 36.725523

As you can see there is no real way to optimize massive string concatenation in PHP :-\