How the setting "Incomplete registrations count against Capacity/Inventory for __ minutes after their last modification" works
Definition
Incomplete registrations count against Capacity/Inventory for __ minutes after their last modification is a setting that reserves inventory for registrants who start but do not complete the form.
This setting tracks registrants in memory while the form is incomplete.
Behavior and limits
If registrants stop the form flow and the time limit is reached, the items selected by registrants (agenda items or sessions) are canceled and returned to the inventory pool.
Because registrants consume system memory, there is a limit on the number of spots available for each form.
The slot limit can range from 150 to 900, depending on current system resources.
When the slot limit is reached, registrants see a notice that the form is unavailable, and the system checks every 10 seconds to see if a spot has freed up.
Configuration guidance
When Plan > Options > "Incomplete registrations count..." setting has a value of 5,000 minutes, if an incomplete registration does not continue through the form to the Confirmation page, it will take up one of these system memory spots for 83 hours.
The system default of 10 minutes is usually sufficient.
If more is needed, increasing to 30 or 60 minutes is often all that would be necessary.
When setting the time, consider how long a registration may pause in the form.
Consider how long the inventory should remain unavailable and how many people are expected to register in that timeframe.
The higher the time set, the longer the incomplete registration can pause on the form but limits the number of registrations that can access the form simultaneously.
The higher this value is set and the more people you expect to register, the more likely registrants will see the form as unavailable and will need to wait to register.
Note
Proper management of the above settings for the event should help avoid this issue.