Innodb存储引擎的缓存命中率计算

数据库的慢查询是我们在生产环境中必须经常检测的，如果慢查询语句过多，说明我们应该增加buffer_pool的大小了。常常检查的指标就是查看缓存命中率是否过低。

mysql> show status like 'innodb_buffer_pool%';
+---------------------------------------+--------------------------------------------------+
| Variable_name                         | Value                                            |
+---------------------------------------+--------------------------------------------------+
| Innodb_buffer_pool_dump_status        | Dumping of buffer pool not started               |
| Innodb_buffer_pool_load_status        | Buffer pool(s) load completed at 190107  7:19:16 |
| Innodb_buffer_pool_resize_status      |                                                  |
| Innodb_buffer_pool_pages_data         | 31732                                            |
| Innodb_buffer_pool_bytes_data         | 519897088                                        |
| Innodb_buffer_pool_pages_dirty        | 0                                                |
| Innodb_buffer_pool_bytes_dirty        | 0                                                |
| Innodb_buffer_pool_pages_flushed      | 1298499                                          |
| Innodb_buffer_pool_pages_free         | 1024                                             |
| Innodb_buffer_pool_pages_misc         | 8                                                |
| Innodb_buffer_pool_pages_total        | 32764                                            |
| Innodb_buffer_pool_read_ahead_rnd     | 0                                                |
| Innodb_buffer_pool_read_ahead         | 0                                                |
| Innodb_buffer_pool_read_ahead_evicted | 0                                                |
| Innodb_buffer_pool_read_requests      | 438699486                                        |
| Innodb_buffer_pool_reads              | 536971                                           |
| Innodb_buffer_pool_wait_free          | 42342                                            |
| Innodb_buffer_pool_write_requests     | 237826577                                        |
+---------------------------------------+--------------------------------------------------+
18 rows in set (0.04 sec)

我们需要关注这几个值：Innodb_buffer_pool_read_requests表示read请求的次数，Innodb_buffer_pool_reads表示从物理磁盘中读取数据的请求次数

因此缓存命中率的计算方法是：（1- Innodb_buffer_pool_reads / Innodb_buffer_pool_read_requests） *100 %，如果缓存命中率过低，则我们需要考虑扩充内存的大小或者是innodb_buffer_pool_size的值。