dots-update-groups

Unity DOTS ECS systems showing values one frame late occur when update group assignment and intra-group ordering are incorrect. Choosing the proper SystemGroup and enforcing valid UpdateBefore or UpdateAfter constraints establishes deterministic reader and writer dependencies, preventing delayed visibility.

DeltaTime meaning changes across Unity DOTS update groups based on timing semantics. In fixed-step simulation it represents a fixed timestep, while in variable-rate simulation groups it reflects wall-clock time, meaning the same code can accidentally run with incorrect timestep semantics if placed improperly.

Use UpdateBefore and UpdateAfter for ECS system ordering only when both systems share the same update group. This intra-group peer ordering establishes correct reader and writer dependencies, whereas cross-group ordering traps require different SystemGroup assignments to maintain determinism.

Choose the correct SystemGroup for Unity DOTS by matching timing semantics: Initialization for input setup, Simulation for logic, FixedStep Simulation for deterministic physics, VariableRate for low-frequency ticking, and Presentation for render-side reading to ensure deterministic execution.

Configure RateManager for variable-rate ticking in Unity DOTS ECS by assigning systems to the VariableRate Simulation group. This ensures low-frequency ticking maintains deterministic behavior while correctly handling the timestep semantic changes associated with variable update frequencies.

Unity DOTS physics jitter happens when fixed timestep simulation systems are placed in the wrong update group. Assigning deterministic physics and netcode systems to the FixedStep Simulation group ensures they run at the correct frequency and remain race-free with other simulation writes.