On an Oracle database server, we don't want to see pages or processes being swapped out. You'll notice that when there is plenty of memory to go around, the swap-outs will almost always be zero.

Figure 4-15 is a vmstat report showing zero for both pages swapped in (si) and pages swapped out (so). Just as we want, the swap-out value is consistently zero. If you occasionally see pages being swapped out, that is an indication the system is under some memory pressure. It doesn't necessarily mean there is a problem, but it's getting close. I look at it as if the system is just entering the response-time curve's elbow.

I am commonly asked why I don't look at the pages swapped in and only the pages swapped out. Well, if there are pages being swapped in, there must have been pages swapped out. And if pages have been swapped out, there is a good chance they will eventually be paged back in.