Redo wastage is not a problem. Indeed, it benefits performance by preserving LGWR's sequential I/O pattern. However, high redo wastage is a symptom of a very active LGWR, and that might be a problem. LGWR is expected to be highly active in many instances, but it can be overactive if the log buffer (more correctly, the _log_io_size) is too small, or if the commit rate is too high. If LGWR is overactive, it will place unnecessary load on the redo latches, and on the I/O subsystem. The operating system may also degrade LGWR's execution priority.
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05-Apr-2002 |
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