Returns the number of bytes that this event internally uses in disk storage for the values, not counting the bytes for storing the field names. This does not include the RAM usage of an event during a query, implying that aggregated events will have a size of zero.
The example here searches for large events in the repository:
eventSize() | _eventSize > 10000
You cannot do a direct comparison, as the function augments the event data with the event size information, rather than returning data.