Encountered negative task assignment count for worker node in Scheduler Service logs

[Mario_Petre]

Qlik Sense Scheduler service logs on Central Node may contain the following error:

Encountered negative task assignment count for worker $hostname

Secondary Scheduler nodes periodically send heartbeat signals to the Primary Scheduler node (often same as the Central Node) containing data on their respective workloads and task queues. The Primary Scheduler uses this data to monitor workload across the environment and make load balancing decisions. 

Under certain timing circumstances, depending on task chaining and individual node workload, a Secondary Node may report a task completion even after the Primary Scheduler had already assumed no workload on said node. When the system encounters this circumstance, it logs the message above. In most version of Qlik Sense Enterprise on Windows, this message is only available at DEBUG level, however several versions may still print this message at INFO level.

If a large number of such events is detected on a system, it may indicate the task workload is no longer efficiently spread in the environment and Secondary Nodes are constantly falling out of sync with the Primary Scheduler. A higher frequency of task failures would be expected as a result. 

The Primary Scheduler uses a self-correcting mechanism that realigns these queues over time, however a high frequency of events should be investigated further by the platform administrator. 

Environment

• Qlik Sense Enterprise on Windows February 2021

Resolution

Improvements in the heartbeat messaging mechanism will reduce the frequency of these messages to only those situations where a system administrator should review task loads and assignments or troubleshoot with Support. In most systems, these messages are benign, especially if they appear with high frequency without any other negative impact to the platform. 

Unless actively troubleshooting an issue, it is typically not necessary to keep log verbosity in DEBUG for long periods of time. Since this message is only visible at this verbosity level, simply turn the logging level to INFO or below. 

Information provided on this defect is given as is at the time of documenting. For up to date information, please review the most recent Release Notes, or contact support at support.qlik.com with the QB-4728 for reference.

Fix Version:

Qlik Sense Enterprise on Windows - May 2021 Release

Cause

Product Defect ID: QB-4728