I wrote a while ago about how mext works – it runs “mysqladmin extended-status” and formats it nicely. But what if you want to use it to format saved output that you’ve put into a file? It’s actually very easy. You can tell it what command-line to run to generate its input. By default you are probably going to tell it to run “mysqladmin ext -ri10″ or something like that, but you can just as easily make it run “cat my-saved-output”.

Let’s see how this can be useful. Imagine I have a server that stalls every now and then, and I’ve set up mk-loadavg to watch for this and capture information about system activity with a script that contains

$ mysqladmin ext -c 30 -i1 > mysqladmin-output.txt

That’ll gather 30 samples one second apart. Now I’ll format it:

$ wget -q http://www.maatkit.org/mext
$ sh mext -r -- cat mysqladmin-output.txt | less -S

I’m piping the output into less -S so that I can see unwrapped output. 30 samples of mysql status variables are going to be aligned in columns next to each other, so without the -S flag I’ll probably see something unhelpful.

If you have a hard time visualizing the above, go ahead and run the commands! It’ll take only a minute, and it’ll make a lot more sense to you then. This is a really useful way to summarize and understand what is going on (or has gone on) inside your MySQL server.

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