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How to increase the number of threads available?

· One min read

ClickHouse uses threads from the Global Thread pool to process queries and also perform background operations like merges and mutations. If there is no idle thread to process a query, then a new thread is created in the pool.

The maximum size of the global thread pool is determined by the max_thread_pool_size setting, which defaults to 10,000. You can modify this value in your config - here we set it to 20,000:


If you modify max_thread_pool_size, we recommend changing thread_pool_queue_size to be the same value. The thread_pool_queue_size setting is the maximum number of jobs that can be scheduled on the Global Thread pool:


You can also free up resources if your server has a lot of idle threads - using the max_thread_pool_free_size setting. The default is 1,000, which means your Global Thread pool will never have more than 1,000 idle threads. The following example increases the value to 2,000:


Check out the docs for more details on the settings above and other settings that affect the Global Thread pool.