v.21.6Improvement
Set background_fetches_pool_size to 8 for improved production performance
Setbackground_fetches_pool_sizeto8that is better for production usage with frequent small insertions or slow ZooKeeper cluster. #22945 (alexey-milovidov).
Why it matters
This change improves ClickHouse's handling of background fetch operations by increasing the thread pool size. It addresses performance bottlenecks encountered in production settings, especially when many small insertions occur or when interacting with slow ZooKeeper clusters, resulting in better throughput and stability.How to use it
To apply this improvement, set the configuration parameterbackground_fetches_pool_size to 8 in your ClickHouse server settings. This can be done by adding or modifying the parameter in the server configuration file (e.g., config.xml) or via dynamic settings if supported. No additional changes are required in query syntax.