Backtraces

Backtraces

Backtraces, Fatal-Error Backtraces and Reading a Stack Trace

debug_backtrace() returns the chain of calls that led to the current line as an array of frames, debug_print_backtrace() prints it, and every exception records one (getTraceAsString()). New in PHP 8.5, fatal_error_backtraces (on by default) adds a trace to true fatal errors such as memory exhaustion, which used to report only a file and a line.

export.php: debug_print_backtrace() and a PHP 8.5 fatal-error backtracePHP

<?php
function exportOrders(string $format, int $rows): string {
    debug_print_backtrace();                    // who called me, and with what
    $out = '';
    for ($i = 0; $i < $rows; $i++) $out .= str_repeat('x', 1024);
    return $out;
}
function nightlyJob(string $date): void { exportOrders('csv', 1_000_000); }
ini_set('memory_limit', '4M');
nightlyJob('2026-09-23');

Output

#0 /home/dev/shop/export.php(8): exportOrders('...', 1000000)
#1 /home/dev/shop/export.php(10): nightlyJob('...')
PHP Fatal error:  Allowed memory size of 4194304 bytes exhausted (tried to allocate 2093088
  bytes) in /home/dev/shop/export.php on line 5
Stack trace:
#0 /home/dev/shop/export.php(8): exportOrders()
#1 /home/dev/shop/export.php(10): nightlyJob()
#2 {main}

The message names the failing line (5). Frame #0 is the innermost call, and export.php(8) means called from line 8; each frame is one step further out, down to {main}. Production settings hide arguments ('...'); the development values show exportOrders('csv', 1000000). Mark a password parameter #[\SensitiveParameter] (Built-In Attributes) to keep it out of every trace.

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