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This article mainly explains "how to understand the log file sync and log file parallel write of oracle". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "how to understand the log file sync and log file parallel write of oracle".

Log file sync and log file parallel write are the problems in the log competition. Frequent commit triggers this wait event. If you don't commit too often, but you also see this kind of wait event, here are some common reasons:

1. Physical equipment reason: the equipment storing redo is old and its performance is poor, so it needs to be updated.

2.redo files conflict with other hot files: the redo log should be placed on a dedicated device, otherwise there will be varying degrees of competition when other files want to write to the device at the same time as LGWR; so to avoid this, redo files should be placed on dedicated devices

3. The log is placed on a buffered device. Because oracle itself does a redo log buffer to redo, such a double-buffer condition will slow down the log write speed. The buffer of reading and writing related devices can be changed according to the system and storage devices.

4. The storage technology is selected incorrectly. For example, using RAID-5 is normally used as a storage raid1 for redo.

The perfect way is to use multiple disks to store redo files. For example, disk A stores the group1.3,B disk and the group2.4,C disk holds the archive log. When the group1 is full, LGWR will work on the group2. At this point, the ARCn process works on group1. In this way competition can be avoided. The above waiting events can be avoided.

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