Oracle Metric log buffer space

Oracle Tips by Burleson Consulting

The log buffer space Oracle metric indicates that the process is waiting for space to become available in the log buffer (Space becomes available only after LGWR has written the current contents of the log buffer to disk.) This typically happens when applications generate redo faster than LGWR can write it to disk.

MetaLink note 216205.1 Database Initialization Parameters for Oracle Applications 11i, recommends a log_buffer size of 10 megabytes for Oracle Applications, a typical online database:

The log writer parameters control the size of the log buffer within the SGA and how frequently the redo logs are check pointed ( all dirty buffers written to disk to create a new recovery point).

A value of 10MB for the log buffer is a reasonable value for Oracle Applications and it represents a balance between concurrent programs and online users. The value of log_buffer must be a multiple of redo block size, normally 512 bytes.

The popular Ion tool is the easiest way to analyze Oracle log file behavior over time (above plot of log file parallel writes), and Ion allows you to spot hidden redo log performance trends. Ion is our favorite Oracle tuning tool, and the only 3rd party tool that we use.

This, and many other Oracle performance metrics are discussed in my book "Oracle Tuning" by Rampant TechPress. You can buy it directly from the publisher and save 30% at this link:

http://www.rampant-books.com/book_2005_1_awr_proactive_tuning.htm

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