PHP error guide

PHP "Allowed memory size exhausted": What It Means and How to Fix It

fatal fatal Affects: All PHP versions Last verified:

Error summary

The request exceeded `memory_limit`. Raise the limit only after reducing peak usage—unbounded arrays, huge file loads, and debug dumps are the usual causes.

What it means

The request exceeded memory_limit. Raise the limit only after reducing peak usage—unbounded arrays, huge file loads, and debug dumps are the usual causes.

What the error means

PHP’s memory manager refused a further allocation because the script hit the configured memory_limit for that SAPI.

Why PHP produces it

PHP isolates request memory so one runaway script cannot take the whole machine. Fatals occur at the allocation that crosses the limit.

PHP version notes

CLI and FPM often have different memory_limit values—verify with php -i vs a phpinfo page for the pool.

Most common causes

  • Loading entire large files/result sets into arrays
  • Infinite recursion or rapidly growing structures
  • Composer/vendor operations with low CLI memory
  • Debug tools holding large object graphs

Minimal examples

BAD — reproduces the problem

php 
$all = file_get_contents('/var/log/huge.log');\n$lines = explode(\"\\n\", $all);

FIXED — safer pattern

php 
foreach (new SplFileObject('/var/log/huge.log') as $line) {\n    // process\n}

Step-by-step diagnosis

  1. Note the byte limit in the message (e.g. 134217728 = 128M).
  2. Confirm which php.ini/memory_limit applies to the failing SAPI.
  3. Profile the hot path—exports, image processing, ORM hydration.
  4. Check for accidental nested loops appending without bounds.

Fixes

Fix #1: Stream or chunk work

Process rows/files incrementally instead of building giant arrays.

php 
$fh = fopen($path, 'rb');\nwhile (($line = fgets($fh)) !== false) {\n    process_line($line);\n}\nfclose($fh);

Fix #2: Raise limit carefully

Increase memory_limit for a known heavy job, preferably per-script, after reducing usage.

php 
ini_set('memory_limit', '256M'); // prefer pool/job-specific config in production

Common mistakes when fixing it

  • Setting memory_limit = -1 globally in production
  • Raising limits forever instead of fixing a leak/unbounded export

How to prevent it

  • Chunked exports and generators
  • Memory budgets in CI for heavy commands

Web server / environment notes

FPM workers also constrained by system RAM and `pm.max_children`

Tags: cli,fpm,wordpress,composer

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