Database / Milvus Vector database Interview questions
What is the difference between Strong and Bounded Staleness consistency in Milvus?
Strong consistency guarantees a search always reflects every write that had committed before the search was issued, no exceptions, which requires the search to wait for confirmation that all relevant recent writes are visible before returning. Bounded Staleness relaxes that guarantee slightly: a search may return results that are stale by up to a configured time window, trading a small, bounded amount of freshness for potentially lower latency and higher throughput.
| Strong | Bounded Staleness |
| Always reflects the absolute latest committed writes. | May lag behind by up to a configured, known window. |
| Can incur higher latency, waiting for the latest state. | Generally lower latency, since it doesn't need to wait for the absolute latest state. |
| Best for cases where stale reads would be genuinely problematic. | Best when a small, bounded lag is acceptable for better performance. |
An application updating inventory counts right before checkout might need Strong consistency to avoid overselling; a social media feed's semantic search, where a few seconds of staleness is imperceptible to users, is a natural fit for Bounded Staleness instead, trading that small, controlled amount of freshness for meaningfully better throughput under load.
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