Using IBM's AIX dialect of UNIX, an I/O bound database server is usually evidenced by a high value in the wa (wait) column of vmstat. In the next listing, we see that 22 percent of the CPU time is being used waiting for database I/O.

L 5-19

root> vmstat
kthr     memory             page              faults        cpu
----- ----------- ------------------------ ------------ -----------
r b   avm   fre re pi po fr   sr cy in   sy cs us sy id wa
0 0 217485   386 0   0   0   4   14   0 202 300 210 14 19 45 22

It is important to note that a high wait value does not always signal an I/O bottleneck. The CPU wait could be due to other factors, and this metric simply means that the CPU is waiting for external OS services.

Now that we understand the basics of the vmstat utility, let's explore an easy method for capturing vmstat data, storing it inside an Oracle table, and producing server performance reports.

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Detecting Potential I/O Bottlenecks in AIX

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