Oracle Performance Tuning Tips

Hold log files open

Holding the log files open

The greatest potential for tuning the speed of a log switch is in the opening of the new log file members. The operating system's open() system call is much faster if another process already has an open file descriptor on the same file. This is partly because certain information about the file is already cached in kernel memory. But more importantly in the case of raw logical volumes, it avoids a delay while logical volume state data reflecting the opening of the raw logical volume is written to the volume group reserved area on disk.

The APT script hold_logs_open.sh is intended to be run daily from cron under Unix to hold all the log files for an instance open for the next 24 hours. The first time we tried this technique, it shaved an impressive 6 seconds of the speed of each log switch. Your mileage will vary depending on your logical volume or file system and kernel configuration, but it is sure to help a little.