max_thread_pool_free_size
If the number of idle threads in the Global Thread pool is greater thanmax_thread_pool_free_size, then ClickHouse releases resources occupied by some threads and the pool size is decreased. Threads can be created again if necessary.
Example
max_thread_pool_size
ClickHouse uses threads from the Global Thread pool to process queries. If there is no idle thread to process a query, then a new thread is created in the pool.max_thread_pool_size limits the maximum number of threads in the pool.
Example