How to configure ClickHouse for optimal usage of available RAM?

Shiv Iyer
Posted on March 28, 2023

Configuring ClickHouse for optimal usage of available RAM is critical for achieving optimal performance. Here are some tips for configuring ClickHouse to make the most of available RAM:

  1. Adjust the max_memory_usage parameter: The max_memory_usage parameter determines the maximum amount of RAM that can be used by a single query. You can adjust this parameter to optimize the balance between query performance and available memory. If you have plenty of RAM available, you can increase this parameter to improve query performance. However, if you have limited RAM, you should decrease this parameter to avoid excessive swapping.
  2. Configure memory usage for caching: ClickHouse uses memory for caching data to improve query performance. You can adjust the max_memory_usage_for_all_queries parameter to control the amount of RAM available for caching. If you have plenty of RAM available, you can increase this parameter to improve cache performance. However, if you have limited RAM, you should decrease this parameter to avoid excessive swapping.
  3. Use memory-mapped files: ClickHouse can use memory-mapped files to avoid loading data into RAM until it is actually needed. This can help reduce the amount of RAM needed for data storage. You can enable memory-mapped files by setting the use_mmap parameter to true.
  4. Use appropriate compression algorithms: Compression can reduce the amount of data that needs to be stored in RAM, but different compression algorithms have different performance characteristics. You should choose the compression algorithm that best suits your data and workload. For example, the LZ4 algorithm is optimized for speed, while the ZSTD algorithm is optimized for compression ratio.
  5. Use appropriate storage engines: ClickHouse offers several storage engines, each with its own performance characteristics. You should choose the storage engine that best suits your data and workload. For example, the MergeTree engine is optimized for time-series data, while the ReplacingMergeTree engine is optimized for data with updates and deletes.
  6. Use appropriate data types: ClickHouse supports a wide range of data types, including numeric, string, and date/time data types. Choosing the appropriate data types can help reduce the amount of RAM needed for data storage. For example, using integer data types instead of floating-point data types can reduce the amount of RAM needed for storing numerical data.
  7. Use appropriate block size: ClickHouse processes data in blocks, and the block size can have a significant impact on RAM usage. You should choose a block size that balances the overhead of block processing with the benefits of data locality. The max_block_size parameter controls the maximum size of a single block.
  8. Use appropriate query optimization techniques: ClickHouse supports various query optimization techniques, including indexing and partitioning. You should choose the optimization techniques that best suit your data and workload. For example, indexing can improve query performance by reducing the amount of data that needs to be read from disk, while partitioning can improve query performance by reducing the amount of data that needs to be scanned.
  9. Use appropriate hardware: ClickHouse performance is influenced by the hardware configuration, including the number of CPU cores, amount of RAM, and storage type. You should choose hardware that is appropriate for your data and workload. For example, using solid-state drives (SSDs) can improve query performance by reducing disk I/O latency.
  10. Monitor and optimize memory usage: ClickHouse provides various tools for monitoring memory usage, including the max_memory_usage and max_memory_usage_for_all_queries parameters, as well as the system.events and system.metrics tables. You should monitor memory usage regularly and adjust the configuration settings as necessary to avoid excessive memory usage and swapping.
  11. Use memory-efficient data formats: ClickHouse supports various data formats, including CSV, JSON, and Parquet. Choosing a memory-efficient data format can help reduce the amount of RAM needed for data storage. For example, using a binary data format, such as Parquet, can reduce the amount of RAM needed for storing data.