Now that it has been a couple of months since Magento 1.9.1 was released we have had enough experience upgrading from older versions of Magento to 1.9.1 to discuss what we have found to be the important things to keep in mind when upgrading to that version. We have found that two major issues impact the upgrade:
Sending Emails Now Relies on the Magento Cron Job
One of the under the hood changes made in 1.9.1 is that most emails to be sent out are first placed in queue and then the queued emails are sent the next time the cron job for Magento is run. If you do not have a cron job configured or enabled (as was the case for one website we dealt with) then many emails, including order confirmation and transactional, will not been sent out.
If you are having a problem with emails not being sent in Magento 1.9.1 you can check if unsent queued emails are the problem by reviewing the core_email_queue table, which contains the emails that have been added to the queue. Once the cron job has run the “processed_at” value for emails will have the time that they were sent and if they have yet to be sent they will not have a value set for that.
During testing of the upgrade you will also need to make sure that the cron job is set up for the test installation as well.
PHP 5.3.0 or Newer Is Required
Up until version 1.9 the bare minimum version of PHP that Magento permitted was 5.2.0, in version 1.9.1 that has been increased to 5.3.0. For most part this isn’t an issue considering that PHP 5.3.0 was released in June of 2009 and the listed minimum PHP versions for Magento 1.9.1 is 5.4. Where it can cause an issue is if you are doing an upgrade from the very old Magento 1.3, which wasn’t designed to support PHP 5.3. If you are doing the test of the upgrade in the same server environment as the production website and you can’t use multiple versions of PHP at the same time you will need to either modify the existing Magneto installation to support at least PHP 5.3 or do the upgrade in two stages (first upgrading to 1.9, then changing the PHP version, and then doing the upgrade to 1.9.1).