Performance, testing, and debugging

Measure stages

Bookmark and time separately:

• snapshot gathering and lock/quiesce time;
• SaveGame object construction and validation;
• game-thread serialization;
• worker/platform write and callback latency;
• read latency;
• game-thread object creation/deserialization;
• migration, asset resolution, world travel, actor apply, and post-load rebuilds;
• payload bytes and record counts by subsystem.

Async persistence prevents the device IO from blocking the game thread, but UE 5.8 still serializes/ creates SaveGame objects on the game thread. Use Unreal Insights and packaged target builds to enforce a snapshot/serialization hitch budget.

Test matrix

• first boot, new profile, overwrite, manual/autosave rotation, delete;
• every supported released schema and a multi-version skip upgrade;
• newer/unknown, wrong class, truncated, bit-corrupt, zero-byte, oversized, duplicate-ID saves;
• removed/renamed definition, missing optional content, changed map/actor class;
• disk/quota full, read-only, permission/native UI denial, unplug/suspend/kill at each boundary;
• rapid requests, save during load, travel, death, logout, and stale callbacks;
• multiple local/platform users, account switch, split screen, offline/cloud conflict;
• dedicated/listen server authority, disconnect/reconnect, idempotent backend retry;
• Development/Test/Shipping packaged builds and every target platform.

Never ship migration code without immutable real-world fixtures and expected post-migration assertions. Keep a diagnostic command/UI to report slot metadata and result codes without exposing payload secrets.