On occasion you see these questions. Can I run X number of host instances? What will happen? Without diving deep into the reason why you think you need to, or the details of what is happening inside BizTalk Server when you do, I will present some results of doing that.
First, I needed a machine to play around with. I also wanted a reasonably powerful machine, so I where better to go than to Windows Azure? I selected a BizTalk Server 2013 Evaluation Edition pre-configured image.
Choose the Extra Large size – that’s 8 cores and 14 GB of RAM.
When that machine was provisioned for me, this was how the performance of it looked:
Now I am fully aware that viewing only the Task Managers idea of the processor is a very limited view of “performance” but I am purposefully using that view so that you, the reader, understand that this is NOT intended to be a DeepDive. It is merely an indication.
So, I configured a script I have to create 100 hosts and host instances for me, along with handlers for FILE Adapter for those hosts. But so far no ports and no traffic. This is how that looked.
You can see the Processor churning away at about 20% utilization, while Memory is largely unaffected.
Taking it one step further I wanted to make sure that the host instances actually had something to check for, so I created 1 receive port and 100 send ports. One send port for each of the host instances (the Send Port has that hosts handler for the FILE transport).
That put the machine under a little more pressure. Obviously it is doing something more when it actually has ports configured. Processor is at ~60%. Memory again not really affected.
Remember now, this is all just doing nothing at this point. Let’s see what happens if we actually do something:
That piece of the graph marked in blue above, that’s when I dropped a file into the receive port and receive location that all the 100 send ports (one for each of the hosts) were subscribed on. It went to 100% quickly. All files went through quickly though, and the event didn’t last long enough for BizTalk to start throttling.
So what about the Memory though. Is that really not affected? How much does a BizTalk instance use and wont 100 of them make an impact? Well, it turns out that each host instance will, at this particular point, only use about 20 MB.
But ok, 100 host instance is a lot. What about 50? Still the same config as above, but only 50 host instances are started.
A bit jagged, but still, running only 50 takes Processor utilization down from 60% to 20%. Now what if we send something through?
A short spike when sending the document through to its 50 subscribers.
Taking a little bit of a deeper look at that spike we can see that SQL Server is the main contributor to that spike.
Hmmm. Ok, “But” says the customer, I want all of this to be Low Latency. 50 ms polling. Do it!
CPU goes up from ~20% to a little under 40%. But it also changes characteristics. When it before was jagged, it now becomes more or less a straight line. The processor does not get to rest, and it does not get spikes in the same way.
Unless of course you send a message through, in which case it does again spike.
But it’s just a very short spike. Nothing at all in the way that you can or cannot say that this would be a bottleneck based on this simple test. I have not done any extended tests to see what the MST would be for this machine.
What if we raise the number of host instances just slightly? To 75.
See that marked point in time above? That’s where I enabled the host instances. Proc goes to about 60%. 100 again you say? Let’s try it…
Again a visible increase in power needed. And the proc now at about 70% and pretty flat.
Sending a message through again spikes it.
And SQL is the thing that is grabbing most of that processing power.
So there you go. That’s what would happen if you run 100 hosts and 100 host instances on a single machine, and if you put them all to poll the database at 50 ms.
This was done on a Windows Azure Virtual Machine with the BizTalk Server Evaluation image in its default configuration. I did nothing to it. No updates, no tuning, no alterations. I know for certain that I can improve the performance of what we see above.
You can draw your own conclusion from the above. My own conclusion is “in-conclusive” ;). That is - I can see that running 100 host instances with 50ms polling on a machine where both BizTalk and SQL share the same machine and the machine is not optimized does not bring down the machine by the share volume of polling alone. However when running even simple traffic through we hit the roof. If this load would be placed on a distributed environment, with SQL and BizTalk on separate machines and SQL with a more optimized storage architecture etc, BizTalk with other configuration such as Global Tracking disabled etc, I should think that the scenario is doable.
I would however highly question why you think you need 100 hosts and 100 host instances. There are a lot of functionality in BizTalk, for example SSO Affiliate Applications, that solve some of the reasons why you would think you need that many. My recommendation is certainly not to go there unless absolutely necessary.