Composer out of memory (allowed memory size exhausted)

1. About the error
2. Why do I see this error
3. Solution
4. Make sure you're on Composer 2
5. Add swap space (the proper fix on a small VPS)
6. Raise the memory limit for one command
7. Prefer require over update where you can

#About the error

Running composer update or composer require fails with:

PHP Fatal error: Allowed memory size of 1610612736 bytes exhausted (tried to allocate ...)

Dependency resolution is memory-hungry. To pick compatible versions, Composer compares every candidate version of every package against all the others, and large or conflicted dependency trees can exhaust the available memory.

#Why do I see this error

• A big dependency tree, or composer update resolving everything from scratch.
• A small server with little RAM and no swap configured.
• An old Composer 1.x install, version 1 used far more memory than version 2.

#Solution

#Make sure you're on Composer 2

Composer 2 cut memory use dramatically. Check and upgrade:

composer --version
composer self-update --2

#Add swap space (the proper fix on a small VPS)

If proc_open(): fork failed or the out-of-memory error shows up on a low-RAM server, the machine simply has no headroom. Adding swap solves it durably without raising PHP limits. See the dedicated guide on adding swap space on Ubuntu.

#Raise the memory limit for one command

To get unblocked immediately, run Composer with an unlimited limit just for that invocation:

COMPOSER_MEMORY_LIMIT=-1 composer update

Or point Composer at a php.ini with a higher limit:

php -d memory_limit=-1 /usr/local/bin/composer update

#Prefer require over update where you can

composer require some/package resolves a smaller slice of the tree than a full composer update, and composer install against an existing composer.lock barely uses any memory at all. On production you should only ever run composer install, never update:

composer install --no-dev --optimize-autoloader