# Objective
Scheduling low cost systems has significant overhead due to task pool
contention and the extra machinery to schedule and run them. Event
update systems are the prime example of a low cost system, requiring a
guaranteed O(1) operation, and there are a *lot* of them.
## Solution
Add a run condition to every event system so they only run when there is
an event in either of it's two internal Vecs.
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## Changelog
Changed: Event update systems will not run if there are no events to
process.
## Migration Guide
`Events<T>::update_system` has been split off from the the type and can
be found at `bevy_ecs::event::event_update_system`.
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Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>
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