Expressions that use a large amount of memory can cause performance problems, both for that particular expression and possibly even the system as a whole. To prevent this, the Memory Circuit Breaker will automatically detect expressions that use too much memory and abort those evaluations to prevent the application server from running out of resources. Only the offending expression fails when the circuit breaker is tripped, allowing all other evaluations to complete successfully.
The threshold for the Memory Circuit Breaker is set at 100,000 AMUs, though that may change in the future. Based on our analysis of actual expression evaluations, this would abort less than 0.01% of all expression evaluations. This threshold is constant regardless of the max heap space configurations for your site, so the only way to avoid the circuit breaker is to modify your design.
It is important to design expressions to limit their memory footprint to ensure they will always evaluate successfully. All functions will use some amount of memory during evaluation, but some design patterns will use more memory than others or retain that memory for a longer period of time.
Memory Circuit Breaker