Oracle 等待事件之 db file scattered read
db file scattered read 官网解释: This event signifies that the user process is reading buffers into the SGA buffer cache and is waiting for a physical I/O call to return. A The Check the following
on a healthy system,physical read waits should be the biggest waits after the idle waits. However,also consider whether there are direct read waits (signifying full table scans with parallel query) or db file scattered read waits on an operational (OLTP) system that should be doing small indexed accesses. Other things that could indicate excessive I/O load on the system include the following:
解释:db file scattered read 等待事件:是由于多数据块读操作产生的,当我们检索数据时从磁盘上读取数据到内存中,一次I/0读取多个数据块,而数据块在内存中是分散分布并不是连续的,当数据块读取到内存中的这个过程就会产生“db file scattered read” 事件。 多个数据块读场景: (1) FTS(Full Table Scans) 全表扫描 (2) IFFS(Index Fast Full Scans) 索引快速全扫描: 把索引链切割成很多份,多块并行读取。 (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |