Practice
1. In the cache warming system, at step 3 the Cache Loader fetches data from the database. What happens if the database response is delayed beyond the configured timeout?
easy
Solution
Step 1: Trace Cache Loader timeout behavior
On timeout, Cache Loader skips warming that key to avoid blocking the entire warming process.Step 2: Eliminate retry and fallback options
Indefinite retries block warming; fallback cache is not part of warming design; null writes risk stale data.Final Answer:
Option C -> Option CQuick Check:
Timeout causes skipping key warming to maintain overall progress [check]
Hint: Timeout skips key warming to avoid blocking cache load [check]
Common Mistakes:
2. In the file sync system's upload flow, at Step 4 the Delta Upload Worker receives chunk hashes from the client. What does the worker do when it finds a chunk hash already stored on the server?
easy
Solution
Step 1: Trace Delta Upload Worker behavior at Step 4
When the worker finds a chunk hash already stored, it skips re-uploading the chunk to save bandwidth and marks it as present.Step 2: Eliminate incorrect behaviors
Requesting resend wastes bandwidth; deleting existing chunks breaks deduplication; re-chunking is unrelated to upload step.Final Answer:
Option A -> Option AQuick Check:
Delta Upload Worker skips existing chunks to avoid redundant upload [check]
Hint: Skip chunks with known hashes to save bandwidth [check]
Common Mistakes:
3. If the trace context extraction component is missing in a downstream service, what is the exact failure observed in the distributed trace?
medium
Solution
Step 1: Understand missing context extraction impact
Without extracting trace context, the downstream service cannot link its spans to the parent trace, so it starts a new root trace, breaking the trace continuity.Step 2: Eliminate other failure modes
Spans are not merged incorrectly; they are disconnected. Spans are still recorded locally, so not lost entirely. Trace collector accepts spans but sees them as separate traces.Final Answer:
Option A -> Option AQuick Check:
Missing extraction causes new root trace, breaking linkage [check]
Hint: No extraction -> new root trace breaks parent-child links [OK]
Common Mistakes:
4. At 10x scale, which component in a Write-Through caching system is most likely to become the bottleneck first, and why?
hard
Solution
Step 1: Identify Write-Through bottleneck
Write-Through synchronously writes to DB on every write, increasing DB load linearly with scale.Step 2: Compare other components
Cache handles fast reads; network bandwidth usually sufficient; app servers block but DB saturation causes overall failure first.Final Answer:
Option C -> Option CQuick Check:
DB synchronous writes bottleneck Write-Through at scale [check]
Hint: Write-Through sync DB writes bottleneck at scale [check]
Common Mistakes:
5. At 10x traffic scale, which component in a GeoDNS-based global traffic distribution system is most likely to fail first and why?
hard
Solution
Step 1: Identify GeoDNS scaling bottleneck
GeoDNS servers handle DNS queries globally; at 10x scale, query volume spikes, and short TTLs reduce cache hits, increasing load.Step 2: Eliminate other options
Authoritative DNS servers (A) are stateless per query. Data center load balancers (C) scale horizontally and are not the first bottleneck. Network routers (D) handle Anycast well at scale.Final Answer:
Option B -> Option BQuick Check:
GeoDNS query load spikes with limited caching cause first failure [check]
Hint: GeoDNS query load spikes first due to limited caching [check]
Common Mistakes: