Vmstat

Before changing this, make sure you run vmstat enough to determine that there really is a considerable amount of context switching going on.

Unlike vmstat or iostat, the defaults usually do not give you as much information as you probably would like.

At the beginning of the script, we choose vmstat 1 as the command to be executed and read from every second.

You need to understand this concept when trying to interpret the output of commands, such as vmstat and sar.

You should actually use vmstat to identify the cause of your bottleneck, even before you have determined that it might be memory related.

If interval is specified, vmstat will summarize system activities over the last interval in seconds repeatedly.

The next section of code creates a pipe from the vmstat command, where the program will read data once per second.

After waiting a few seconds for the FluidSynth program to activate, the processing of vmstat output can begin.

The vmstat command is typically run in a separate xterm window in the foreground with the output going to the terminal.

Part 2 of this series discussed vmstat in great detail, which is one of our favorite VMM monitoring tools.

Part 2 of this series discussed vmstat in great detail, which is one of my favorite VMM monitoring tools.

The next day I get another call and start vmstat again (see Listing 2).

netstat is really not a monitoring tool in the sense of vmstat and iostat.

At the operating system level the sar, vmstat, and top commands are a good place to start to verify basic system hygene.

The vmstat command reports information about a system's memory usage and statistics about VMM operations like page replacement.

If no parameters are specified, vmstat only lists previous statistics about the system and won't refresh.

The vmstat output does not provide information about computational file pages.

The chordStats program will read the vmstat program from standard in, and write the note events -- unbuffered -- to FluidSynth's stdin.

We like to use this command for quickly troubleshooting an issue, especially when we want a little more than vmstat on my screen.

The vmstat avm column shows ALL the virtual memory that is accessed, even if it is not paged out.

We noted these figures in a spreadsheet, which we used later to analyze the vmstat logs.

Note: These statistics were generated from 2-second-interval vmstat logs that we ran during the test procedure.

Time interval specifies the interval vmstat refreshes, and count specifies the maximum times it will refresh.

The vmstat command measures and records CPU and virtual memory usage during the tests.

One simple way to modify chordStats is to replace the vmstat command with an event generator that refreshes faster.

Use the vmstat command for a closer examination of memory.

If a count is given, vmstat will pull system statistics repeatedly until it reaches the number of count times specified.

The following code sample shows the vmstat output as the test program kept on consuming memory.

I might use an interactive tool, such as vmstat, and then a capturing tool, such as nmon, to help me track data historically.

After restarting the LPAR as a shared memory partition, I used lparstat and vmstat to view the LPARs' shared memory settings.

Let's return to the vmstat output and what is wrong with your system.

With the output from vmstat, the primary thing to look at is the paging information.

UNIX platforms use command line utilities like IOSTAT and VMSTAT.

The field headers bi (blocks in), bo (blocks out), and us (user CPU usage), are read from the vmstat program every second.

It's important to make the distinction between this and what is reported back in vmstat.

We use the vmstat program for simple system status monitoring.

This information was taken by examining top and vmstat logs.

The important fields from the vmstat output are shown below.

You probably already use certain commands, such as vmstat or topas, and are familiar with ways of identifying processes that are CPU hogs.

We see topas as a graphical type of vmstat.

The type of information reported by svmon is slightly different than vmstat.

One can look at the context switching using either the vmstat or sar commands.

However, after the program had allocated around 100MB, we could see increased paging activity from vmstat.

The following table correlates sar and vmstat descriptives (see Table 1).

Recall that vmstat 1 generates a list of values every second.

Let's look at the more important fields to analyze in the vmstat output.

All UNIX systems provide tools such as ps and vmstat to provide process and virtual memory statistics.

You should start with the old standby, vmstat.

The vmstat output in Figure 4 below shows a system in great pain.

Begin a 2-second interval vmstat log on the test machine.

You can get this information using vmstat -P ALL, as seen here in Listing 4.

See Listing 1 for an example of running vmstat.

Table 1. sar output fields and the corresponding vmstat field