Metadata is a short record which captures main characteristics of an entire data record or objects inside each data record. These characteristics appear to be useful when one needs to find a necessary record as fast as possible, without reading the entire data records. Read Metadata article.
Let us consider a script which fills an event record with many events. It can look as
In this example, event consists of 3 data containers with Poisson random numbers. We write all such events into a file. in a zipped serialized form. How to insert a data record characterizing the sum of 3 random values, x+y+x, such that after reading this small record one can navigate to the necessary event without running over all 50000 events?