計算邏輯位於函式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<ulong>(MAX_BUFFER_POOLS),
				static_cast<ulong>(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<ulong>(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;
	}
```

- 小於1G那麼 instance為1，這個時候cleaner執行緒也是1</ulong></ulong></ulong>

MySQL:一段innodb buffer instance和cleaner執行緒計算邏輯

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