What is a Hash Collision?

Difficulty: 5/10

hash functions, collision resolution, performance impact

Hash Collision

A hash collision occurs when two different keys produce the same bucket index, or more generally the same hash value. Collisions are unavoidable in practical Hash Tables because the key space is usually much larger than the number of available buckets. A Hash Table therefore needs a collision-resolution strategy.

javascript

1
Different keys can legitimately map to the same bucket.
2
Separate chaining stores multiple entries in the same bucket.
3
Open addressing searches for another available slot.
4
High collision rates increase lookup cost.
5
A good hash function reduces collisions but cannot eliminate them completely.

Scenario Questions

0-2 years experience

2-5 years experience

1We saw a spike in lookup latency for our session cache and the logs show many keys ending up in the same bucket. How would you investigate and fix a possible hash‑collision issue?

Follow-up Questions