按官方手册推荐Innodb buffer Hit Ratios的计算是:
| 100-((iReads / iReadRequests)*100) iReads : mysql->status->Innodb_buffer_pool_reads iReadRequests: mysql->status->Innodb_buffer_pool_read_requests |
出处: http://dev.mysql.com/doc/mysql-monitor/2.0/en/mem_graphref.html
搜”Hit Ratios”
推荐有兴趣的同学把这个页面都看一下应该也会有很大收获.
另外在hackmysql: www.hackmysql.com网站上的: mysqlsqlreport中关于buffer命中计算是:
| $ib_bp_read_ratio = sprintf "%.2f", ($stats{'Innodb_buffer_pool_read_requests'} ? 100 - ($stats{'Innodb_buffer_pool_reads'} / $stats{'Innodb_buffer_pool_read_requests'}) * 100 :0); |
即:
| ib_bp_hit=100-(Innodb_buffer_pool_reads/Innodb_buffer_pool_read_requests)*100 |
另外我们知道查看Innodb Buffer Hit Ratios的地方是:
Buffer pool hit rate : XXXX/1000;
那个XXX/1000即是buffer pool hit ratios的命中.
这样也可以从代码里看一下这个bp命中计算:
| storage/innobase/buf/buf0buf.c # void buf_print_io storage/innodbase/include/buf0buf.h #struct buf_block_struct |
在buf0buf.c 中的buf_print_io函数中可以看到:
| void buf_print_io( … if (buf_pool->n_page_gets > buf_pool->n_page_gets_old) { fprintf(file, "Buffer pool hit rate %lu / 1000n", (ulong) (1000 - ((1000 * (buf_pool->n_pages_read - buf_pool->n_pages_read_old)) / (buf_pool->n_page_gets - buf_pool->n_page_gets_old)))); } else { fputs("No buffer pool page gets since the last printoutn", file); } buf_pool->n_page_gets_old = buf_pool->n_page_gets; buf_pool->n_pages_read_old = buf_pool->n_pages_read; … } |
结合:
storageinnobaseincludebuf0buf.h中
| struct buf_block_struct{ … ulint n_pages_read; /* number read operations */ … ulint n_page_gets; /* number of page gets performed; also successful searches through the adaptive hash index are counted as page gets; this field is NOT protected by the buffer pool mutex */ … ulint n_page_gets_old;/* n_page_gets when buf_print was last time called: used to calculate hit rate */ … ulint n_pages_read_old;/* n_pages_read when buf_print was last time called */ … |
从这个来看innodb buffer hit Ratios的命中计算需要本次取的值和上次值做一个减法公式应该为
| ib_bp_hit=1000 – (t2.iReads – t1.iReads)/(t2.iReadRequest – t1.iReadRequest)*1000 |
t(n): 时间点 两个时间间隔最少是30秒以上,在小意义不大.
