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Why is That First WCF Operation SO Slow?

By Steve Ives, Posted on June 25, 2015 at 12:06 pm

If you have ever developed and worked with a WCF service you may have noticed that the very first time you connect to a newly started instance of the service there can sometimes be a noticeable delay before the service responds. But invoking subsequent operations often seems almost instantaneous. Usually the delay is relatively short, perhaps even just a fraction of a second, but still noticeable. Well earlier this week I encountered a WCF service that exhibited this behavior, but the delay for the first operation was almost three minutes! Something had to be done.

Some time later, after much debugging, web searching and more than a little head scratching, we realized that the “problem” that we were seeing was actually “by design” in WCF and was related to the generation of metadata for the service. It turns out that if “metadata exchange” is enabled for the service then WCF generates the metadata, regardless of whether anyone is currently requesting it or not, at the time that the first operation is requested by a client. Often the generation of the metadata takes almost no time at all, but as the size and complexity of a service grows (in terms of the number of operations exposed, the number of parameters, the number and nature of complex types exposed, etc.) the time taken to generate the metadata grows. In the case of this particular service there were over 800 individual operations defined, with lots and lots of complex types being exposed, and the service was still growing!

The only time you need metadata exchange enabled is when you need to access the WSDL for the service, so in simple terms whenever you need to do an “Add Service Reference” or “Update Service Reference”. The rest of the time having it enabled is just slowing things down at runtime.

I can’t tell you exactly how to enable and disable metadata exchange with your service, because there are several different ways it can be configured, but it’s likely going to be one of these:

  1. A <serviceMetadata/> token used in the <serviceBehaviors> section of a Web.config or App.config file.
  2. An <endpoint/> token that uses the IMetaDataExchange contract defined in a <service/>section of a Web.config or App.config file.
  3. Code that does the equivalent of one of the two options above.

So the lesson learned was to enable metadata exchange only when it is needed, for the purpose of creating or updating client proxy code; the result was an almost instantaneous response from the service once metadata exchange had been disabled. Of course it goes without saying that metadata exchange should NEVER be enabled on production services.


Old Dog … New Tricks … Done!

By Steve Ives, Posted on June 3, 2015 at 3:59 pm

The old adage tells us that you can’t teach an old dog new tricks. But after the last three days, I beg to differ! It’s been an interesting few days for sure; fun, challenging, rewarding and heated are all words that come to mind when reflecting on the last few days. But at this point, three days into a four-day engagement, I think that we may just have dispelled that old adage. For one this “old dog” certainly feels like he has learned several new tricks.

So what was the gig? It was to visit a company that has an extensive application deployed on OpenVMS, and to help them to explore possible ways to extend the reach of those applications beyond the current OpenVMS platform. Not so hard I hear you say, there are any number of ways of doing that. xfServerPlus immediately comes to mind, as do xfODBC and the SQL Connection API, and even things like the HTTP API that could be used to allow the OpenVMS application to do things like interacting with web services. All true, but there was one thing that was threatening to throw a “spanner (wrench) in the works”. Did I mention that the application in question was developed in COBOL? That’s right, not a line of DBL code anywhere in sight! Oh and by the way, until about a week ago I’d never even seen a single line of COBOL code.

Now perhaps you understand the reason that challenging was one of the words I mentioned earlier. But I’m up for a challenge, as long as I think I have a fighting chance of coming up with something cool that addresses a customers needs. And in this case I did. I didn’t yet know all of the details, but I figured the odds of coming up with something were pretty good.

Why all of this confidence? Well, partly because I’m really good at what I do (can’t believe I just said that), but seriously, it was mainly because of the fact that a lot of the really cool things that we developers just take for granted these days, like the ability to write Synergy .NET code and call it from C#, or write VB.NET code and call it from Synergy .NET, have their roots in innovations that were made 30+ years ago by a company named Digital Equipment Corporation (DEC).

You see OpenVMS had this little thing called the Common Language Environment. In a nutshell this meant that the operating system provided a core environment in which programming languages could interoperate. Any language that chose to play in that ball park would be compatible with other such languages, and most languages on OpenVMS (incuding DIBOL and DBL) did just that. This meant that BASIC could call FORTRAN, FORTRAN could call C, C could call PASCAL and … well you get the idea. Any YES it means that COBOL can call DBL and DBL can call COBOL. OK, now we’re talking!

So why is this such a big deal? Well it turns out that Digital, later Compaq, and later still HP didn’t do such a great job of protecting their customers investments in their COBOL code. It’s been quite a while since there was a new release of COBOL on OpenVMS, so it’s been quite a while since OpenVMS COBOL developers had access to any new features. This means that there isn’t a way to call OpenVMS COBOL routines from .NET or Java, there isn’t a way for OpenVMS COBOL code to interact with SQL Server or Oracle, and there isn’t an HTTP API … so don’t even think about calling web services from COBOL code.

But wait a minute, COBOL can call DBL … and DBL can call COBOL … so YES, COBOL CAN do all of those things … via DBL! And that fact was essentially the basis for my visit to Toronto this week.

I’m not going to get into lots of details about exactly what we did. Suffice it to say that we were able to leverage two core Synergy/DE technologies in order to implement two main things:

  1. A generic mechanism allowing COBOL code executing on OpenVMS to interact with Windows “stuff” on the users desktop (the same desktop that their terminal emulator is running on).
  2. A generic mechanism allowing Windows “stuff” executing on the users desktop to interact with COBOL code back on the OpenVMS system.

The two core technologies have already been mentioned. Outbound from OpenVMS was achieved by COBOL calling a DBL routine that in turn used the Synergy HTTP API to communicate with a WCF REST web service that was hosted in a Windows application running in the users system tray. Inbound to OpenVMS was of course achieved with a combination of xfNetLink .NET and xfServerPlus.

So just who is the old dog? Well as I mentioned earlier I probably fall into that category at this point, as do several of the other developers that it was my privilege to work with this week. But as I set out to write this article I must admit that the main old dogs in my mind were OpenVMS and COBOL. Whatever, I think that all of the old dogs learned new tricks this week.

It’s been an action packed three days but I’m pretty pleased with what has been accomplished, and I think the customer is too. I have one more day on site tomorrow to wrap up the more mundane things like documentation (yawn) and code walkthroughs to ensure that everyone understands what was done and how all the pieces fit together. Then it’s back home on Friday before a well deserved vacation next week, on a beach, with my wife.

So what did I learn this week?

  1. I really, really, REALLY don’t like COBOL!
  2. OpenVMS was WAY ahead of its time and offered LOTS of really cool features. Actually I didn’t just learn this, I always knew it, but I wanted to recognize it in this list … and it’s MY BLOG so I can Smile.
  3. Synergy/DE is every bit as cool as I always believed; and this week I proved it to a bunch of people that had never even heard of it before.
  4. New fangled elevators are very confusing for old dogs!

UX Design; Elevator Controls

By Steve Ives, Posted on June 1, 2015 at 3:09 pm

Those of you who attended the recent DevPartner conference in Philadelphia will no doubt remember the excellent presentation on UX Design that was given by guest speaker, Billy Hollis. During his presentation Billy cited photographs of a couple of elevator control panels. He used one as an example of bad design, the other an example of good.

I won’t show the actual photos that Billy used (sorry, you had to be there for that!) but in a nutshell the layout of the buttons and other information (floor numbers, etc.) on the first panel was at best confusing. There was clear physical evidence that users had been confused by the panel and frequently had not understood how to operate the elevator!

The second example was much a much better panel design. The designer had successfully used techniques such as visually grouping related things together in a way that made the correct operation of the elevator a much more obvious task … intuitive even.

Well, upon arriving at a customers office building in Toronto, Canada earlier today I encountered an elevator control panel that, for me at least, took the confusion to a whole new level.

I should make it clear that the elevator in question was one of a cluster if four in the lobby of a shared office building, and that I was arriving at the customer site at about the same time that everyone was arriving at work. The point is that the lobby was pretty busy at the time, it wasn’t as simple as just walking up and pressing an “I want to go up” button.

No problem I thought, it may be two or three elevator cars before I get to make the final step of my journey up to the 4th floor. I’m a few minutes early and all is good.

image1Finally my turn came, I waited while a few other people stepped on, then I took my place in the elevator car. Intuitively I spun around to determine whether one of my elevator buddies had already pressed the 4th floor button, and I was ready to press it myself if not. The panel opposite is what I encountered.

Now I like to think of myself as a reasonably bright guy, so I instantly figured it out; the buttons would be on the OTHER SIDE of the door. And I was correct … well … kind of. I glanced to the opposite side of the elevator door … and saw an identical panel on that side too!

Not wanting to appear totally inept I just waited quietly until the other people got off at their (somehow) chosen floors … and no, unfortunately nobody else was going to 4.

The doors swished closed and I was finally alone in the elevator. I don’t remember exactly what my out loud remark to myself was, but I believe it started something along the lines of “WHAT THE ….”. So, patiently I waited and sure enough after a little while the doors once again swished open and I was back where I started from in the lobby!

I’ll be honest with you, I was getting a little “pissed” at this point (excuse my language, but its true). But not wanting to appear like a total fool I stepped away as if I had intentionally returned to the lobby, and waited for the crowd to clear … all the time subtly (I thought) observing to see HOW THE HECK THESE FREAKING ELEVATORS WORKED!!! And then … I saw it … everything instantly became clear. The floor selector buttons were indeed on the other side of the elevator door … they were on the OUTSIDE!!!!

IMG_0957Yep … believe it or not in this building you need to indicate which floor you want to go to BEFORE you step on to the elevator. After you have stepped on it’s too late; way too late!

And further, having selected your intended destination on the small tough-screen display in the lobby you are then instructed WHICH of the four elevators (conveniently labeled A, B, C and D) you should step onto in order to reach your desired floor!

Actually this is a pretty clever system, but other than the fancy 6” touch screen display there was absolutely nothing to indicate that anything was different here. Brilliant system but totally unintuitive … and so very frustrating for first-time users. Which I guess was one of the points that Billy was making in the first place.


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