How to Implement Metrohash Function in ClickHouse for High Performance


The MetroHash function implemented in ClickHouse offers performance benefits and low collision rates, contributing to the efficiency of hash-based operations.

Features of Metrohash function in ClickHouse

Here’s how the MetroHash function achieves these advantages: 

  1. Performance:
  • MetroHash is designed to provide excellent performance characteristics. It is optimized for speed and efficiency, making it well-suited for high-performance hash-based operations in ClickHouse. 
  • The MetroHash function leverages efficient hash algorithms, such as MurmurHash and CityHash, which are known for their fast execution and low computational overhead. 
  • ClickHouse utilizes MetroHash’s optimized implementation to efficiently hash the join key values during the construction of hash tables and the probing phase of the Hash Join algorithm. 
  • The high-performance nature of the MetroHash function contributes to faster data processing and query execution in ClickHouse, leading to improved overall performance of hash-based operations. 
  1. Low Collision Rates:
  • Collision occurs when different input values produce the same hash value. High collision rates can adversely impact the performance and accuracy of hash-based operations. 
  • The MetroHash function in ClickHouse is specifically designed to achieve low collision rates. It employs advanced techniques and algorithms to minimize the likelihood of collisions. 
  • MetroHash uses a combination of hashing methods, including the use of both 64-bit and 128-bit hash states, to achieve a good distribution of hash values and reduce collision probabilities. 
  • By minimizing collisions, ClickHouse ensures accurate and efficient hash-based operations, such as hash table construction and hash table probing in the Hash Join algorithm. 
  • Low collision rates enable ClickHouse to accurately and efficiently match rows during join operations, leading to reliable query results and improved performance. 


ClickHouse’s implementation of the MetroHash function offers unparalleled performance and precision, leveraging optimized hash algorithms to accelerate data processing while minimizing collision rates. This ensures efficient and reliable hash-based operations, making ClickHouse ideal for high-performance analytics at scale.

To know more about functions in ClickHouse, do read the following articles:

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About Shiv Iyer 225 Articles
Open Source Database Systems Engineer with a deep understanding of Optimizer Internals, Performance Engineering, Scalability and Data SRE. Shiv currently is the Founder, Investor, Board Member and CEO of multiple Database Systems Infrastructure Operations companies in the Transaction Processing Computing and ColumnStores ecosystem. He is also a frequent speaker in open source software conferences globally.