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Distributed Systems
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Two replicas cannot communicate. Clients must read the latest completed write regardless of which replica they contact. What may be necessary to preserve this guarantee?
AReturn the most recent value according to the client's clock.
BReject or delay requests on a side unable to establish freshness.
CAcknowledge writes on both sides and compare their timestamps later.
DServe each side's local value and reconcile after reconnection.
A CDN has a fresh cached copy of a public image. The origin is temporarily unreachable. What can the CDN normally do for this image?
AServe the fresh cached response without contacting the origin.
BWait for origin recovery before serving any cached response.
CInvalidate the image because the origin failed a health check.
DQuery the origin database directly to reconstruct the image.
A large table is frequently queried with WHERE email = ?. No relevant index exists and EXPLAIN shows a sequential scan. What is the most direct optimization?
AAdd an index on a rarely filtered description column.
BIncrease the API's JSON response compression level.
CAdd read replicas before examining the access path.
DAdd an appropriate index on email and verify the new plan.
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