Amazon Neptune Gets Online Index Rebuild—Defrag Your Graph DB Without Downtime
Amazon Neptune Database now lets you rebuild indexes on the fly to reclaim wasted storage and boost query performance, all while keeping read and write operations running smoothly. This feature works across all Neptune regions on provisioned instances starting with engine 1.5.0.0, giving you fine-grained control over rebuild speed and workload impact through tunable concurrency settings.
source: [aws/whats-new]