change some parameter's default value: brpc_num_threads from -1 to 256 compaction_task_num_per_disk from 2 to 4 compaction_task_num_per_fast_disk from 4 to 8 fragment_pool_thread_num_max from 512 to 2048 fragment_pool_queue_size from 2048 to 4096 --------- Co-authored-by: yiguolei <yiguolei@gmail.com>