Magento 1.9.2.4 Download File Size is Very Large – Where is Magento 1.9.2.1?

The attack vector you should worry about is not certain user pressing F5 for 5 minutes or a day but any program or script that automatically calls your website. Setting a connection limit prevents from high load on the server which can be caused by a DoS (Denial of Service) attack.

max_user_connections is the maximum number of simultaneous connections permitted to any given MySQL user account (your MySQL-user seems to be admin). The default value for max_user_connections is 0 (which means "no limit", see MySQL documentation).

If your are on a shared host who has set this limit for your webspace, there will be (hopefully) a valid reason.

One reason for this setting to be applied on shared hosting could be that it prevents other clients services if one of the clients on the shared host gets DoS-attacked. It does not kill the whole (MySQL-)Server in this case.

Update: I overread that you do testing in a local VM. So you this configuration is up to you. You can adjust the limit in /etc/my.cnf

Ways of coping with it:

• Adjust your setting on your local VM.
• If on shared hosting: Talk to your provider if he can/wants to raise the limit for you (if he can)
• For the live webshop: Move to a dedicated server where you can control and adjust these settings
• Caching can help to reduce the number of requests to your database-server
• Check the var/report directory and empty old reports regularly or even better: Set up monitoring which checks the var/report directory for the amount of files and gives you a warning.
• Regarding the "ugly page": The error-report page can be adapted to your webshop-design.

It's a problem with method aliasing in subclasses.

tl;dr

For version CE 1.9.1.0 you can try to patch app/code/core/Mage/SalesRule/Model/Rule/Condition/Product/Combine.php at line #219 turning

$valid = $children && $this->validate($children[0]);

into

$valid = $children && self::validate($children[0]);

For other versions, find the above line inside the validate method.

Explanation

Mage_SalesRule_Model_Rule_Condition_Product_Subselect::validate() overrides the Mage_SalesRule_Model_Rule_Condition_Product_Combine::validate() and calls the parent implementation along the way. Too bad the latter eventually tries to call itself when met with rule validation on configurable products, but ends up calling the overriden implementation instead, so an infinite loop is started.

Warning

The quick fix proposed is consistent with the core SalesRule models but might break more complex class hyerarchies introduced by third party modules.