Allow max_server_memory_usage change without restart

Why it matters

This feature enables administrators to adjust the maximum server memory usage limit on-the-fly, improving server manageability and flexibility. It eliminates downtime caused by restarts when tuning memory usage parameters, thus enhancing operational efficiency and resource optimization.

How to use it

Users can modify the max_server_memory_usage setting dynamically via the server configuration or administrative interfaces without restarting the ClickHouse server. The change will take effect immediately, allowing for seamless adjustment of memory usage limits.