分类： Oracle
2013-02-20 09:25:01
To interpret the buffer cache hit ratio, you should consider the following:
解释缓存的命中率,你应该解释如下:
Repeated scanning of the same large table or index can artificially inflate a poor cache hit ratio. Examine frequently executed SQL statements with a large number of buffer gets, to ensure that the execution plan for such SQL statements is optimal. If possible, avoid repeated scanning of frequently accessed data by performing all of the processing in a single pass or by optimizing the SQL statement.
重复的扫描同样大表或索引可以人为的提高缓存的命中率,检查,重复的执行sql语句得到大量的缓存数量.确保执行sql性能是最理想.如果可能 ,避免重复扫描频繁访问的数据进行通过在一个单一的处理或优化SQL语句。
If possible, avoid requerying the same data, by caching frequently accessed data in the client program or middle tier.
如果可能避免查询相同的数据,缓存经常访问的数据在客户端程序或中间层.
Oracle blocks accessed during a long full table scan are put on the tail end of the least recently used (LRU) list and not on the head of the list. Therefore, the blocks are aged out faster than blocks read when performing indexed lookups or small table scans. When interpreting the buffer cache data, poor hit ratios when valid large full table scans are occurring should also be considered.
在一个长的完整表的扫描是成块存取的是lru的最后面的而不是放在列表的头.因此,当索引执行查找或小表扫描,块不会很快的被老化比块读.当对高速缓存中的数据进行解释时,可怜的命中率,有效的对大表进行扫描也应该被考虑.
In any large database running OLTP applications in any given unit of time, most rows are accessed either one or zero times. On this basis, there might be little purpose in keeping the block in memory for very long following its use.
在一个运行oltp的应用程序的 大型的数据库中在任何时间,绝大部分的行被使用一次或0次.在这个基础上,他们可能有很小的目的保持块在内存一段很长的使用时间.
A common mistake is to continue increasing the buffer cache size. Such increases have no effect if you are doing full table scans or operations that do not use the buffer cache.
一个通常 的错误是继续增加高速缓存的大小,如果你在执行一个全表的扫描或操作增加是没有影响的,因为没有使用高速缓存.
7.2.3.1 Increasing Memory Allocated to the Buffer Cache
增加高速缓存的内存分配
As a general rule, investigate increasing the size of the cache if the cache hit ratio is low and your application has been tuned to avoid performing full table scans.
作为一个一般的规则,如果缓存的命中率很低和你的应用需要避免对一个表的执行全表扫描,可以考虑增加缓存的大小.本文转自cuug网
