Load Testing – No excuses just many compromises!
So you’ve decided to roll-out SAP ‘xyz’ solution, and it’s going to add what you suspect to be a decent amount of load, requiring you to purchase and tune hardware and software to support it. But do we have time to load test the solution?
Are you kidding me?
This is like running a functional test for the first time with one user and saying – yes – that all works – put it in production (which also happens from time to time unfortunately).
The remainder of this blog is to help those who need to think about doing some level of load testing without calling in the load test professionals. e.g. No excuses just compromises.
Commercially Focused Load Testing
So what does it take to do Load Testing. Well it depends…Not an “it depends” and I won’t give you an answer but a “it depends” because load testing can be a make or break for some projects. e.g. If you are rolling out a customer website like Apple, Amazon, Google would do; then you are going to have to do a lot of work to do load testing properly. And while I can give you philosophical answers to what to do, get an expert in load testing (but keep on reading anyway if you like)!
So what else does it depend on, well obviously, how much load is expected to be seen (no use doing load testing if it’s 2-3 users concurrently with a few background jobs – this would just be called testing it properly if this was an issue). How about visibility, risk to business (or alternatively efficiency gains if testing quick response times), how quick you can react to issues if something does go wrong, etc.
So if you think load testing would be worthwhile, and your overall risk profile isn’t too great plus you find yourself debating whether to do load testing because of the cost; then I say – let’s do it but compromise.
Things you’ll need:
- A production like system with as near as final software as possible (sized similar, with as close to production batch jobs, configuration as possible). Plus a good proven backup of this system before you run load tests!
- A good idea of the # of different types of users that will be hitting the system concurrently – and in extreme cases a more detailed hour by hour breakdown of expected load (e.g. Payroll, BI and Bill Run loads running concurrently at 1am can be fun)
- 1 or maybe more test machines located near the servers but which covers the end to end systems being performance tested (e.g. If you are going via a reverse proxy and you are concerned about where the bottleneck may be, then you’ll need to test beyond the reverse proxy). Go with 2000 real users per test machine as a guide
- A good set of real scenarios that cover off the various components and technologies, and avoid caching and locking. e.g. Managers looking at the Universal Worklist, Employees raising a trip request, displaying a BI report, searching on a document, posting a document, etc. Note – Avoid large downloads like files as this will limit your ability to emulate load since it effectively soaks up the network on the test machines.*
- A download of jMeter (jmeter.apache.org) with the additional plug ins (https://code.google.com/p/jmeter-plugins/) to give us some fancy graphs and emulators. Note – If you can afford HP LoadRunner, then it’s easier to learn (I always go to type Lode Runner for those raised in the 80’s)
- A coder/tester who understands how HTML works (I wish this was any coder now days) and how to use developer tools within browsers (ditto)!
- Basis and infrastructure volunteers to monitor your load testing. And just in case, you may need a couple of CAB’s approved for comms as you just never know what will happen to the business!
* My main point here is that emulating real production load is futile in most cases, so sure – do some specific performance testing of big custom builds, or get a bunch of users hitting the system at once for application concurrency issues, but let’s just focus load testing on ensuring we have the right infrastructure, basis and application parameters set-up to give your stakeholders confidence that if anything goes wrong with load and go-live – that it’s likely to be a specific application issue.
So with all this, you can complete the following:
- A Load Testing Plan (to keep stakeholders happy) – but this is a quick document describing the things we’ll need – and should be fit for purpose – I had SAP offering to review my load testing document over 5 days for something that took a day to write!
- Get your developer going through some training material to learn jMeter!
The key is to breakdown the different user types, and assign them relevant pauses between “clicks” (according to an old SAP Note 651581, SAP states this is typically ~7 seconds for “well experienced” users and 20 seconds for less experienced ones – not sure they have seen my mother in law in front of an iPad but hey). Then potentially a different wait time between end to end transactions. Put this into your test plan, and now we’re good to go.
I’m a big fan of jMeter. It’s got a lot of power and mostly intuitive. Maybe not quite as user friendly as Loadrunner. There’s quite a bit already out there in SCN about jMeter, but I’ll just add some cool things I noticed and give some lessons lessons from the SAP based testing I did. Topics I’ll cover:
- Threadgroups with jMeter Plug-Ins and Documentation
- Different User Threadgroups
- Arghh – Web Dynpro Dynamic Parameters
- Recording Scripts Through Built-In Proxy
- Random Timer
- NWBC and SAPGUI
- Load Versus Stress Testing
- HTML Request/Response Parameters to Care About
- What Happened at “n” Minutes???
- Search and Replace
- Chrome Tools and StackEdit
- Ah – So Pretty!
Threadgroups with jMeter Plug-Ins and Documentation
I use threadgroups as a way of grouping the different types of users. Using the jMeter plug-ins, you can use a stepping threadgroup which not only makes it easy to progressively increase the # of users to the maximum number over a period of time, then maintain that number of a little longer (to soak the system a little) then gradually roll the individual threads off; but it also gives you a graph you can cut and paste into your test plan like so:
Different User Threadgroups
As I hinted in the previous point; threadgroups are great to separate the user groups. Example below which makes reporting easy to split by group:
If you capture all the metrics to a file, you can analyse the results any time. You can try to display a pretty graph while running the scripts to monitor the progress (e.g. Response times) but if you were running for an extended time or looking at a substantially large test scenario, you’ll probably chew up all memory in jMeter before you hit performance issues.
Arghh – Web Dynpro Dynamic Parameters
This is the most ugly part of the work I did. I discovered that Web Dynpro (ABAP) is really bizarre when it comes to writing HTML scripts. In short, unless you do something about it, Web Dynpro parameters are dynamic and incredibly difficult to program for. The solution? Very well hidden (but discoverable in Service Markeplace if you look for automated testing) parameter called sap-wd-stableids. Luckily due to the community, I found this which helped describe it a little further:
This all said, for some scenarios, I still couldn’t take a script I recorded in one system and use it in another system without re-recording the script. I did try and change all references (refer to search and replace below), but for some Web Dynpro screens, there was more to it than just this parameter id. As Abdul states in his reference above; it’s not guaranteed to work in all cases.
Recording Scripts Through Built-In Proxy
Okay – This is a bit 101 for jMeter users, but just pointing out to you that you can make a proxy in jMeter which you then point your browser at, and run through the required scripts. This then effectively builds you a shell of a script to start to adapt for your testing. Just pointing out that you don’t need to hand build these very low level scripts.One lesson learned – put a filter on the recorder as you don’t need to download jpg’s, CSS files, etc within load testing.
Obvious, but just to be clear, use the Gaussian Random Timer between “clicks” and not HTML calls to provide a random response time. Users responding every 7 seconds exactly isn’t realistic. I would suggest a random delay between 2 and 19 seconds would be more realistic – hence this timer should be used.
Simple lesson here – record without SSL, and switch to SSL for the load test. And if you are afraid to use SSL, refer to this blog:
NWBC for Desktop and SAPGUI
Yep – These are thick clients and won’t work with jMeter. So what do we do? We compromise. Use NWBC for HTML and WebGUI/ITS. It will add more load to SAP than expected but that’s fine – it’s load testing and our tests are really not going for perfection.
Getting access to write your load tests in any system just isn’t going to happen, so building your scripts in a way to be moved is another obvious step. 2 of the easier areas to do this:
1. Using user defined variables in the Test Plan (e.g. Time between clicks, Time between transactions) and;
2. Using the config element HTTP Request Defaults which allows you to enter details such as server name port name, HTTP/HTTPS, etc; and have it applied to all requests (called samples) that have blank values for this information.
Load versus Stress Testing
Load test – Testing of expected volume in production.
Stress test – Testing beyond expected volume to the point of failure where failure could simply be an unacceptable response time.
For my scenario, I had a limited number of users in the SAP system, so rather than creating thousands of users, I changed wait times between clicks and transactions to much less – which effectively quadrupled the overall load with a simple tweak of a couple of parameters. It does not give you a perfect idea of how many users you can handle, but it does let you identify bottlenecks in your system. e.g. I compromised to get the job done.
HTML Request/Response Parameters to Care About
When scripting SAP web transactions, there are quite a few parameters to care about that you have to retrieve from a response from SAP and insert into the next request. The most important ones just for reference are (I’ve also included very technical jMeter information which you can ignore unless you need to do this yourself and want some guidance):
XSRF for NWBC: regex used name=”sap-login-XSRF” value=”(.+?)”
- sap-nwbc-context for NWBC: regex used name=’sap-nwbc-context’ value='(.+?)’
- sap-ext-sid for NWBC: regex used sap\\x2dext\\x2dsid\\x3d(.+?)\\x3f followed by a BSF PostProcessor that uses the following: var test = vars.get(“sap-ext-sid”);vars.put(“sap-ext-sid”,test.replace(“\\x2d”, “-“));
- sap-wd-secure-id for Web Dynpro: regex used name=”sap-wd-secure-id” value=”(.+?)”
- sap-contextid for Web Dynpro: regex used sap-contextid=(.+?NEW)
Note – To work out where this happens, you use “View Results in Tree” which captures the request/responses when you run the test so you can reverse engineer and debug the parameter mappings.
What’s happened at n minutes???
So in the middle of my load test, I had a massive spike on response time, and then everything was not going so well. What happened? Well, the point of this point is to not mention the monitoring you should have in place on the server, but to mention that you should also capture relevant statistics via perfmon.exe on your test machine (or equivalent if not Windows). Upon investigation, it looks like a software roll-out occurred at this point, impacting my machine, then the network was impacted from rolling out of software to nearby machines.
Monitoring Results in VMWare
So a week after I finished testing, I asked the infrastructure guys to send through some graphs. Guess what, VMWare averages/sums up details to a granularity of an hour after a week. I can tell you that reporting a graph with a flat line in load testing, is not useful.
Search and Replace
A quick tip about jMeter scripts. They are just text XML files. Hence search and replace in Wordpad or similar is the easiest way to change a hostname throughout.
Chrome Tools and StackEdit
This was a nice surprise – I used StackEdit – a Chrome app add-on during this work and discovered that the cryptic responses you get back from Web Dynpro render nicely in StackEdit so you can see what is happening. To explain, Web Dynpro sends UI commands back to the web page in a very compressed format rather than complete web pages but this makes it visible.
I also made use of some diff tools in Chrome which was handy but not good enough to promote here – still looking for a good one actually.
Ah – So pretty!
Of course, load and stress testing is very technical, and you have stakeholders to please. You need pretty graphs. You’ll obviously get lots of good graphs from Solution Manager or Infrastructure monitoring, but what Stakeholders will most care about is response times for different scenarios. So provided you name the samples well, you can use the Response Times Over Time graph for the selected scenarios you care about (e.g. NWBC login, Refresh Universal Worklist, etc); it makes great graphs for reporting that you can clearly explain.
So what happened for us…
We found we had not changed the default maximum sessions which meant it died at around 200 users the first time we ran the test. We didn’t configure the number of background and update tasks to handle the load expected. We noticed one batch job killing the system (partly due to the previous set-up).
And this was in a system that was meant to be identical to production!
But we applied all the changes into this system and then production and re-ran the tests and all was good in the world (at least for our solution being load tested)! (Compromised) Load and Stress Testing FTW!