What does central node do?

[Huiying]

Hi

Where to find documentation about central node? for example, what does central node do?

Best regards,

Susan

[gustavgager]

There is alot of info in the helpfiles: https://help.qlik.com/en-US/sense/June2019/Subsystems/PlanningQlikSenseDeployments/Content/Sense_Dep...

Basically, the central node is the first node in your environment. Usually its also where you install your repository database (and the other nodes just have the repo service that connect to the central node) and also where you have your fileshare. Its usually also the master scheduler (the one that tells the others what to do).

None of these are mandatory though. You can install postgres somewhere else, you can have the share on a NAS or another node and you can assign the master scheduler to another node.

[Levi_Turner]

The Central Node can do a variety of things in an environment. But the core functionality which the Central node must do includes but is not limited to:

• User synchronization from configured User Directory Connectors (UDCs)
• Database cleanup
• Maintain a record of license usage
• Help deliver extensions
• Migrate apps imported into the environment
• Register new nodes to the environment

[Huiying]

Hi Levi

Thank you for answering. We have 6-node cluster using Qlik Sense 2019June version.

1 central node, 2 engine nodes (one of them is failover), 2 scheduler and 1 proxy.

Currently central node (4 core and 32G RAM) CPU is 60-70%, highest RAM usage is 67%. Min memory usage % in QMC is set to 70.

I'm wondering whether to add more RAM or just increase the min memory usage % in QMC to 80.

2 concerns:

1. some users said apps become slower (cannot investigate as the user didn't provide more information)

2. We are rolling out Qlik Sense solution, so number of APP, user and amount of data are increasing.

But as central node doesn't do the actual rendering, probably the current server is good enough until the RAM usage is above 80%?

 Central node probably doesn't need powerful CPU, but RAM is the constrain?

Best regards,

Susan

[Levi_Turner · Accepted solution]

If the CPU use is in the 60-70% range and the highest RAM use is at 67% then that suggests that (a) the Central's Engine is attached to a virtual proxy (Virtual Proxies > Edit each virtual proxy > Load Balancing) and/or (b) the Central's Scheduler is set to Master & Slave.

(a) means that the Engine is used to deliver end user sessions. (b) means that it does reloads for scheduled tasks.

In terms of increasing the min memory usage, that won't accomplish much. The min/max memory percentages aren't a hard max to the amount of memory the Engine process will use. If the Engine gets a request to open up a massive app which would exhaust the server, it will try to do what is asked of it. The min/max are thresholds for cleaning up types of caching that the Engine does. A lower value will clear up things more to allow for a larger time window between hitting the threshold and total exhaustion.

In the abstract, if the analytic needs for a site are growing and hitting performance bottlenecks, then a site can either:

1. Optimize the applications to require less compute
2. Add more compute

For (1), there's a collection of development best practices collected here by my team.

[Huiying]

Hi Levi

Thank you for the comment. You are right!

Now i removed central node from virtual proxies, and changed scheduler type to Master.

Hopefully the node is more calm. 🙂

And thank you for the toolkit. We will take them to use eventually.

Best regards,

Susan