local write wait等待事件

       最近系统明显变慢。在v$session_wait 发现有个等待事件 local write wait总是出现。分析awr报告，这个等待事件排在第一位。在metalink上搜索这个等待时间的相关信息。没找到什么有用的。      在google上搜素到一篇文章，
      Basically 'local write' wait happens (as the name indicates) when the session is waiting for its local (means writes pending because of its own operation) write operation. This could happen typically if the underlying disc has some serious problems (one of the member disk crash in RAID-05 - for example, or a controller failure). That is why I might have said ' you never see this wait in the normal databases!'. You may see this during (rarely) Truncating a large table while most of the buffers of that table in cache. During TRUNCATEs the session has to a local checkpoint and during this process, the session may wait for'local write' wait. We have not documented this in 'Oracle Wait Interface' as it is very uncommon. May be we can think of adding similar events in the Misc Waits in next edition.
      翻译下： 基本上'local write' wait 表示会话在等待自己的写操作。在磁盘发生严重问题时会发生(例如RAID 5的一个磁盘崩溃,或者磁盘控制器错误),这在正常的系统中极少发生，在TRUNCATE 一个大表而这个表在缓存中的时候，会话必需进行一个local checkpoint,这个时候会话会等待local session wait. 根据我们系统的情况，运行了磁盘检测工具，在日志中发现两个磁盘已经损坏。紧急赶往IDC进行磁盘的更换。

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