Optimize Unity ECS Performance

Contrasts traditional OOP against ECS and DOTS across data layout (scattered versus contiguous memory), processing (per-object versus batched), and scaling (poor with entity count versus linear), and defines the six DOTS building blocks: Entity as a lightweight ID with no data, Component as pure data with no behavior, System as the logic processing components, World as the entity container, Archetype as a unique component combination, and Chunk as the memory block holding same-archetype entities. Ships eight patterns: basic ECS setup, systems with the recommended ISystem interface, entity queries, entity command buffers for structural changes (a Burst-compiled SpawnSystem using a BeginSimulationEntityCommandBufferSystem singleton to defer entity instantiation, component setting, and component addition until the next sync point, plus a parallel-writer variant for use inside an IJobEntity), aspects for grouping related components into cleaner code (a CharacterAspect combining a read-write LocalTransform, a read-only Speed, a read-write Health, an optional Shield component, and an inventory DynamicBuffer behind simple Position and CurrentHealth properties), singleton components, baking for converting GameObjects into ECS entities at build or edit time, and jobs using native collections for Burst-compiled parallel work (a SpatialHashJob implementing IJobParallelFor that hashes each entity's position into a thread-safe NativeParallelMultiHashMap via its ParallelWriter, paired with a SpatialHashSystem that owns the hash map's lifecycle in OnCreate and OnDestroy, resizes its capacity when the entity count grows, and rebuilds it each frame from a query's component data array). Closes with performance tips and a do's-and-don'ts best-practices list.

Use it when building Unity DOTS or ECS gameplay systems, writing ISystem implementations, performing structural changes via command buffers, grouping components with aspects, or converting GameObjects via baking. Skip it for anything unrelated to Unity ECS patterns or outside this scope.

Input is a Unity DOTS gameplay system to implement - spawning, movement, combat, or any mass-simulation behavior; output is the matching C# ECS pattern, such as a system, a query, a command-buffer usage, an aspect, or a baker, ready to drop into a DOTS project.

Built on Unity's Entities package (DOTS): ISystem, SystemAPI, EntityCommandBuffer, IAspect, IJobEntity, and Burst compilation via [BurstCompile] attributes for native-collection-based parallel jobs.

Unity developers building mass-simulation or high-entity-count gameplay with DOTS and ECS who need concrete system, query, command-buffer, and aspect patterns rather than a conceptual ECS-versus-OOP comparison. Particularly relevant once a project's entity count grows past what per-object OOP updates can handle at frame rate, since batched, Burst-compiled processing is what ECS is built to fix.