Preloading+Load Balancing (Qlik May 2025)

[justindallasverizon]

Hello Folks,

I have an app called SomeApp that I am preloading on Server01.  When I go to the virtual proxies listed for Server01, I see {Server01, Server02} listed.  The load balancing algorithm is set to Round-Robin.

My question is: "If SomeApp is preloaded on Server01, will the Round-Robin algorithm STILL send users to Server02 where it is NOT pre-loaded"?

Any help is greatly appreciated.

[Eduardo_Monteiro · Accepted solution]

Yes, the Round-Robin algorithm will still send users to Server02, even though SomeApp is not preloaded there.

Round-Robin load balancing is "session-unaware" — it simply rotates requests across all servers listed in the virtual proxy (in your case, Server01 and Server02) in order, without any knowledge of which apps are preloaded on which engine. Here's what that means practically:

First user → Server01 — SomeApp is preloaded, so it loads instantly.

Second user → Server02 — SomeApp is NOT preloaded. Qlik Sense will still open the app, but it will need to load it into memory on-demand, so that user will experience a longer load time.

Third user → Server01 — back to Server01, fast again.

And so on...

So to directly answer your question: Yes, Round-Robin will still route users to Server02, and those users will not get the benefit of the preload. The preload only helps users who happen to land on Server01.

What you can do about it:

• Preload SomeApp on Server02 as well — this is the most straightforward fix if you want all users to benefit from preloading.
• Remove Server02 from the virtual proxy for this app — if SomeApp should only be served from Server01, only list Server01 in that virtual proxy's load balancing nodes

[justindallasverizon]

Thanks @Eduardo_Monteiro , this answers the questions I had to a tee.

[Eduardo_Monteiro]

Nice, I'm glad to help!

Could you please select my answer as a solution so others could benefit from this topic as well?

Thanks in advance!