Scenario: large Drupal 7 site where cache is extremely slow or fails to clear…
drush cc all
…and eventually PHP runs out of memory (“cannot allocate”).
Check Drush is using the correct version of PHP, it may not be – use
drush status or, more simply:
$ which drush
$ vim /Applications/DevDesktop/tools/drush
# edit the PHP version: [ -z "$PHP_ID" ] && PHP_ID=php7_1
If you’re working on Drupal core or a development site and get this error when running Drush commands, e.g.
drush cr or
PHP Fatal error: Declaration of Drush\Command\DrushInputAdapter::hasParameterOption() must be compatible with Symfony\Component\Console\Input\InputInterface::hasParameterOption($values, $onlyParams = false) in /Applications/DevDesktop/tools/vendor/drush/drush/lib/Drush/Command/DrushInputAdapter.php on line 27
It’s because in the next Drupal minor release (8.4.x) Symfony components have been updated to ~3.2 (in 8.3.x they remain at 2.8.x)
This causes a conflict with Drush – you should upgrade to Drush 9, which you can do via:
composer require drush/drush:9.*
One of several GitHub issues on drush-ops/drush