Which of the following is a property of a good hash function for use in key-value based storage structures?

Question

BlackTom AI · Accepted Answer

Uniform distribution across the output range is the central goal of a good hash function because it minimizes collisions and balances load across buckets or servers. Key relevant concepts: determinism (same input → same hash), avalanche effect (small input changes cause large, unpredictable output changes), low collision probability, uniformity (even spread over output space), and computational efficiency (fast to compute).

Step-by-step reasoning:
1. Purpose of a hash in key-value storage is to map keys to a finite set of buckets/servers. If there are N keys and M buckets, an even mapping yields about N/M keys per bucket on average. This keeps no bucket overloaded and ensures predictable performance.
2. Uniform mapping reduces collisions (different keys hashing to the same bucket). If the hash is uniform, the expected number of keys per bucket is N/M; variance is minimized when distribution is uniform, so hotspots are avoided.
3. The avalanche property is desired: different inputs should produce substantially different outputs (not “very little” difference), which helps uniformity.
4. Computational complexity should be reasonable—hashes must be fast in read/write heavy systems; unnecessary complexity that slows operations is undesirable.

Why the correct option is correct:
- “A good hash function should map its inputs as evenly as possible over the output range” directly states the uniformity/load-balancing property necessary to minimize collisions and evenly distribute keys across storage nodes or buckets.

Why the other options are incorrect:
- “Preferentially distribute output to one server” is wrong because it creates hotspots and poor load balance.
- “With different inputs, a hash function should return output that differs very little” contradicts the avalanche property; similar outputs increase collision risk.
- “A good hash function will involve a complex calculation” is misleading: complexity is not a virtue if it degrades performance; good hashes are efficient while achieving uniformity.

Conclusion: The correct answer is the option stating even mapping across the output range, which matches the provided answer.

Which of the following is a property of a good hash function for use in key-value based storage structures?单项选择题

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