计算逻辑位于函数innobase_start_or_create_for_mysql中 ``` if (srv_buf_pool_instances == srv_buf_pool_instances_default) { #if defined(_WIN32) && !defined(_WIN64) /* Do not allocate too large of a buffer pool on Windows 32-bit systems, which can have trouble allocating larger single contiguous memory blocks. */ srv_buf_pool_instances = ut_min( static_cast(MAX_BUFFER_POOLS), static_cast(srv_buf_pool_size / (128 * 1024 * 1024))); #else /* defined(_WIN32) && !defined(_WIN64) */ /* Default to 8 instances when size > 1GB. */ srv_buf_pool_instances = 8; #endif /* defined(_WIN32) && !defined(_WIN64) */ } } else { /* If buffer pool is less than 1 GiB, assume fewer threads. Also use only one buffer pool instance. */ if (srv_buf_pool_instances != srv_buf_pool_instances_default && srv_buf_pool_instances != 1) { /* We can't distinguish whether the user has explicitly started mysqld with --innodb-buffer-pool-instances=0, (srv_buf_pool_instances_default is 0) or has not specified that option at all. Thus we have the limitation that if the user started with =0, we will not emit a warning here, but we should actually do so. */ ib::info() << "Adjusting innodb_buffer_pool_instances" " from " << srv_buf_pool_instances << " to 1" " since innodb_buffer_pool_size is less than " << BUF_POOL_SIZE_THRESHOLD / (1024 * 1024) << " MiB"; } srv_buf_pool_instances = 1; } if (srv_buf_pool_chunk_unit * srv_buf_pool_instances > srv_buf_pool_size) { /* Size unit of buffer pool is larger than srv_buf_pool_size. adjust srv_buf_pool_chunk_unit for srv_buf_pool_size. */ srv_buf_pool_chunk_unit = static_cast(srv_buf_pool_size) / srv_buf_pool_instances; if (srv_buf_pool_size % srv_buf_pool_instances != 0) { ++srv_buf_pool_chunk_unit; } } srv_buf_pool_size = buf_pool_size_align(srv_buf_pool_size); if (srv_n_page_cleaners > srv_buf_pool_instances) { /* limit of page_cleaner parallelizability is number of buffer pool instances. */ srv_n_page_cleaners = srv_buf_pool_instances; } ``` - 小于1G那么 instance为1，这个时候cleaner线程也是1