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My last series of posts was on some more general rules of thumb around training, so I thought I’d jump next into specifics about technology – specifically, where to find useful information with Tuxedo. I had intended this to be one complete post, but due to the wonderful fractal quality of explaining things, I’ll need to break this up into a series.

For those of you unfamiliar with Tuxedo, this post is unlikely to have much interest or benefit. Before we possibly part ways though, I’ll take a moment to explain exactly what Tuxedo is, as it’s somewhat rarified knowledge nowadays, but the market seems to be pushing to make it and similar products popular again. From my less cynical vantage point, it looks at the moment like a healthy step backwards from making the solution to EVERYTHING a web service, or SOA.

So what is Tuxedo?

Tuxedo is what’s referred to as an Online Transaction Processing system. (OLTP, if you’re looking for a sexy acronym for your new tattoo) It’s also commonly referred to as a Transaction Processing system, but that’s a shorter version of the same thing fundamentally.That means that it processes a huge volume of small operations. Because those operations are things that need to either work or fail consistently, we call those transactions. Transactions can be anything from processing a credit card charge, to updating the location of a package in transit for delivery, to transferring funds between accounts.

One of the big advantages of Tuxedo in particular is that it offers clients a set of available services, each with a unique name. Those services can be provided by a large, complex group of interconnected machines, or all of those services can be provided by one single machine. Clients don’t know and don’t care about the exact location of an available service. They connect to a central point, and request services by name. The exact process that provides that service is unknown to them, which lets you be much more flexible with how you structure the internals of a Tuxedo application.

Because OLTPs are so good at processing these high volumes of transactions (and typically have other technological benefits that make them attractive) they’re used by some big companies, often in preference to newer, ‘cooler’ technology like web services or JEE applications, for example. Just to drop two names, last time I heard both American Express and Fedex were still Tuxedo users.

Thus ends the general part of the post. Thanks for listening!

Now… how to get more useful information out of Tuxedo?

ULOG

The pimp-mack-super-daddy of information in Tuxedo is the ULOG file. This is where Tuxedo logs all of its own information, and also where any calls to the userlog function write data. if you’re having problems with Tuxedo, this should always be your first port of call. By default, the ULOG file lives in the directory pointed to by the APPDIR environment variable. If you haven’t set APPDIR explicitly, then the ULOG file lives in the same directory as your TUXCONFIG file.

The ULOG file is actually a series of files, one for each day. The format of ULOG files is as below:

ULOG.mmddyy

where mm is the current month, dd is the current day of the month, and yy is the last two digits of the current year. Frustratingly, that leaves those files just short of sorting perfectly in chronological order. But I’m sure there’s a solid historical American reason for that convention, possibly involving orange cheese. As it stands, they’ll sort fine inside one year.

You can also control the location of ULOG files with the ULOGPFX environment variable. If you want to keep log files somewhere specific, you can specify a directory and filename like the following:

export ULOGPFX=/var/log/tuxedo/VERYSPECIAL

With that convention, you’d get a file created on the 12th of April 2009 called /var/log/tuxedo/VERYSPECIAL.041209.

Every message that Tuxedo places in the ULOG file comes from a message catalog. You can find a starting point for the Tuxedo message catalog reference in the documentation. Nine times out of ten, if you have some cryptic message in the ULOG file, the message catalog documentation will shed some light on what’s going on, or at least give a hint of the general area of the problem. Unfortunately, one time out of ten, you’ll get a “Contact BEA Support” message, or a repeat of exactly what you’re seeing in the ULOG file.

One thing that gets overlooked sometimes when troubleshooting behaviour between a client and server is that the client gets their own ULOG file too. The same variables (APPDIR and ULOGPFX) control where it’s created. Oftentimes, especially with connectivity issues or situations where nothing appears to be happening in the Tuxedo application itself, it’s the logs for the client and server together that form the complete picture.

TMTRACE: The Firehose

Now, the standard information in the ULOG file is often enough to solve simple problems. But, sometimes a problem comes along that’s complex enough that you need more. That’s where tmtrace comes in. It’s a facility in Tuxedo that allows you to provide more detailed information about what’s happening at runtime. It’s a very lightly documented feature, and I have to confess that my understanding of it borders on hoodoo. But I’ve found that even that hoodoo level of understanding is tremendously useful.

It works on a trace specification, which essentially allows you to specify three things:

  • A trace category, identifying what area of Tuxedo you want more information on.
  • Where you want information to go, which has to be the ULOG file.
  • Whether you want your particular service request to ‘dye’, meaning that all work done as part of your service request will use the same trace configuration you’ve specified, or just use the current configuration for that server.

I’ll explain each of those in a little more detail to shed some light:

The trace category can be as broad as a number of key areas that the documentation provides, or specific as an individual function. Personally, I tend to use the broader areas that are documented, because it means not having to adjust trace specifications constantly. I’m a big fan of the firehose.

The documented categories are:

  • atmi– Specific ATMI functions
  • iatmi – work done implicitly on behalf of an ATMI function, or as part of administration. This is a superset of the atmicategory.
  • xa– work done to manage XA transactions
  • trace – work done related to managing trace functionality

The first three areas tend to be the most useful. In fact, you can just set the firehose to pulverize, use ‘*’, and get everything.

In terms of destinations for trace information, there’s an exciting new change with the more recent versions of Tuxedo: you can now specify utrace as a destination, which can send trace information to a custom destination. That was certainly new to me. The documentation is a little unclear on the specific limits of utrace, and seems to indicate that it can only be used with tmtrace information.

Now, dyeing behaviour. I can set trace configuration as surgically as on a server by server basis. So individual processes can have either their own or no current trace configuration. They could be the quiet, introspective server that lives next door.

Because Tuxedo works on the concept of services, the work done in order to process my service call to process a credit card charge might not be as simple as I think. The one server that takes my service call might make two service calls of its own. One of those service calls might turn into another three service calls.

If we only want to use tracing for a specific flow of logic, to find out what happens with the full flow of processing, using dye allows us to follow processing not just for server A (where we’d set trace) but all the way through to servers D, E and F.

You can set trace configuration either using the TMTRACE environment variable, or using changetrace from inside tmadmin. The simplest way to enable tracing is flick everything on, using changetrace on, or you could just enable tracing for ATMI functions and send trace info to the ULOG file, as follows:

changetrace "atmi:ulog"

For more information on trace specification formats, the best reference is the documentation for tmtrace.

So that’s the ULOG file, and TMTRACE. Both of these together will form the first and and best line of investigation when something is going wrong with your Tuxedo application. Typically, your ULOG file is kind enough to provide some idea of what is going wrong with your application without any additional work. If not, you can coax more useful information out via TMTRACE.

Next up, we’ll have a look at txrpt, and the .TMIB service in Tuxedo – both great tools that provide us with the basics of performance and runtime monitoring in Tuxedo.

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