Just how much IO the log writer background process is generating can be determined from Oracle's instance activity view, v$sysstat. Most IO administrators want Oracle's IO requirements from either an IO operations per second (IOPS) perspective or a megabytes per second (MB/s) perspective. In effect, what they will need to do is ensure the IO subsystem has the capacity to process both Oracle's read and write requirements within acceptable service levels. While every system has its own service level requirements, common service levels are for Oracle reads to be satisfied within 10 ms and writes to be satisfied within 5 ms.

Figure 8-14 shows both the log writer background process IO targeted script and the output. The script accepts the reporting interval as an argument and reports only log writer background process write statistics. Figure 8-15 shows a sample output from a system experiencing severe log file parallel write waits.

Figure 8-14. Shown is a simple log writer background process IO script that will produce both IO operations per second (IOPS) and MB/s. The script takes a single argument of the interval gathering time.