Cache hit rate=((consistent_gets + db_block_gets) - physical_reads) / (consistent_gets + db_block_gets) 2.进一步更精确的结果,我们需要考虑direct reads 如果Buffer hit%为85%,那么如果只是这样简单的按照上面的公式,计算得到85%的命中率,并不意味着miss rate=15%,因为15%中包括我们通常所说的direct ...
Well of course you can name 100% hit rate and all data fits in memory as perfect case but that is not the answer people are looking for. First thing which needs to be understand is – cache hit ratio can be computed differently for different engines. For example for Innodb page hits ar...
20、ffer cache tuning, hit rate, etc1. adjust buffer cache tuning rulesthe goal of tuning: to find data in buffer cache as much as possible, and to reduce the time available for waiting for free blocksdebugging method:wait eventscache hit rationv$db_cache_advice viewadjustment meansreduce the...
10.3.8.2.2 Cache is Too Small It is possible DBWR is very active because the cache is too small. Investigate whether this is a probable cause by looking to see if the buffer cache hit ratio is low. Also use the V$DB_CACHE_ADVICE view to determine whether a larger cache size would be...
1、缓冲池的定义 应用系统分层架构，为了加速数据访问，会把最常访问的数据放在缓存(cache)里，避免每次都去访问数据库。操作系统会有缓冲池(buffer pool)机制，避免每次访问磁盘，以加速数据的访问。MySQL作为一个存储系统，同样具有缓冲池机制，以避免每次查询数据都进行磁盘IO。缓冲池简单来说就是一块内存区域，通过...
这种做法也保证了Buffer Pool可以更专注地实现高效的Cache策略。 Buffer Pool作为一个整体,其对外部使用者提供的其实是非常简单的接口,我们称之为FIX-UNFIX接口[3],之所以需要FIX和UNFIX,是因为对Buffer Pool来说,上层对Page的使用时长是未知的,这个过程中需要保证Page被正确的维护在Buffer Pool中:...
Re: Buffer Cache Hit Ratio Hello,to see the buffer hit rate as it was, say, yesterday,you have to activate the "System Activity Data collector",see the man page for "sadc" for this. It does contain the"crontab" entries you need for this. Thereafter you can call "sar -b" and see...
Buffer Cache is an important component of SGA, which is mainly used to cache data blocks, and its size also directly affects the performance of the system. When Buffer Cache is too small, will cause more Free buffer waits event. The following detailed description of Buffer Cache function, ...
US7249219 * Apr 30, 2004 Jul 24, 2007 Network Appliance, Inc. Method and apparatus to improve buffer cache hit rateUS7249219 * 2004年4月30日 2007年7月24日 Network Appliance, Inc. Method and apparatus to improve buffer cache hit rate...
You need to size your buffer cache so your buffer cache hit rate is optimal for the size of memory you have but not too large so it causes you to get low on memory and start paging and vhand has to shrink the buffer cache.Example 2 GB of buffer cache hit rate 90% 2.5 gb buffer...