A large amount of events (over 4 million) created with name="relationship.rollup" creating a backlog in the sysevent table leading to delay in the processing of other events in the queue.

The reason for the creation of so many events with name="relationship.rollup" was the Out of the box business rule "cmdb synch event"

In out of the box instances, this business rule has the INSERT || UPDATE || DELETE options unchecked in the "When to run" section. If you have all these options checked, whenever any of these operations happen on the cmdb_ci table, the business rule will be triggered, leading to millions of events getting generated.

These options should be used very carefully. Enabling them on a large table like cmdb_ci will surely lead to the creation of millions of these events which would create event queue alerts because of the backlog.

Please find below screenshot of script action for relationship.rollup events which is also Out of the box.

1. To clear out the backlog, Error out these events from the sysevent table so other events can get processed
2. To avoid this issue to reoccur uncheck INSERT || UPDATE ||DELETE options in the "When to run" section for the business rule "cmdb synch event" which is also the Out of the Box setting.

Note: If, for some reason, the options cannot be unchecked as a long term solution then open a new case with Technical Support to see the need to perform a relationship rollup.