most YARN events have timestamp of -1

Most of the YARN events (subclasses of AbstractEvent) have timestamp of -1. AbstractEvent have two constructors, one that initializes the timestamp to -1 and the other to the caller-provided value. But most events use the former (thus timestamp of -1).

Some of the more common events, including ApplicationEvent, ContainerEvent, JobEvent, etc. do not set the timestamp.

The rationale for this behavior seems to be mentioned in AbstractEvent:

  // use this if you DON'T care about the timestamp
  public AbstractEvent(TYPE type) {
    this.type = type;
    // We're not generating a real timestamp here.  It's too expensive.
    timestamp = -1L;
  }

This absence of the timestamp isn't really visible in many cases and therefore may have gone unnoticed, but the timeline service exposes this problem very visibly.