php composer require Error 'Cannot allocate memory'

I'm using composer in symfony 3.4

but when using composer require doctrine/doctrine-fixtures-bundle

always can't install Packages

and it show

mmap() failed: [12] Cannot allocate memory

mmap() failed: [12] Cannot allocate memory

PHP Fatal error: Out of memory (allocated 1199579136) (tried to allocate 150994944 bytes) in phar:///usr/local/bin/composer/src/Composer/DependencyResolver/RuleSet.php on line 90

Fatal error: Out of memory (allocated 1199579136) (tried to allocate 150994944 bytes) in phar:///usr/local/bin/composer/src/Composer/DependencyResolver/RuleSet.php on line 90

I don't know how to fix it