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Don Burleson Blog 









Oracle _log_io_size Tips

by Donald Burleson

Redo log contention is a function of several parameters and the size of the log_buffer.

Steve Adams notes the benefit of the hidden parm _log_io_size:

Most importantly, ensure that LGWR is not overactive because of too low a _log_io_size setting, and that DBWn is not checkpointing recently changed blocks too intensively.

At the application level, beware of spurious COMMITs, avoid SELECT FOR UPDATE statements and before row triggers, and code DML operations to minimize redo generation.

For example, you could set _log_io_size to about 64k or so which typically is a _log_io_size of about 125 log blocks if the log block size is 512. This will have two benefits....

  • The log buffer can handle bigger transactional loads

  • It will stream out redo as it's generated (typically Oracle is very lazy about this.  Oracle will only start writing redo out when the log buffer is about 1/3 full which means that when
    it does write, it's a bursting type of write).




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