ovni/doc/user/concepts/trace-model.md

Trace model

An event model is composed by a group of runtime events

Trace

The information generated by a program or later processed by other ovni tools is known as a trace. A runtime trace stores the information as-is in disk from a program execution. While a emulation trace is generated from the runtime trace for visualization with Paraver.

All the information is always stored inside the same directory, by default ovni/, which is known as the trace directory.

Event

An event is a point in time that has some information associated. Events written at runtime by libovni have at MCV, a clock and a optional payload. The list of all events recognized by the emulator can be found here.

State

A state is a discrete value that can change over time based on the events the emulator receives. Usually a single event causes a single state change, which is then written to the Paraver traces. An example is the thread state, which can change over time based on the events OH* that indicate a state transition of the current thread.

MCV

The MCV acronym is short of Model-Class-Value, which is a three character (byte) identification for events.

Clock

A clock is a 64 bit counter, which counts the number of nanoseconds from an arbitrary point in time in the past. Each event has the value of the clock stored inside, to indicate when that event happened. In a given trace there can be multiple clocks which don't refer to the same point in the past and must be corrected so they all produce an ordered sequence of events. The ovnisync program performs this correction by measuring the difference across clocks of different nodes.

Event model

An event model is composed of several components:

• A set of events all with the same model identifier in the MCV
• The emulator code that processes those events.
• A human readable name, like ovni or nanos6.

Payload

Events may have associated additional information which is stored in the stream.

Binary stream

A binary stream is a file named stream.obs (.obs stands for Ovni Binary Stream) composed of a header and a concatenated array of events without padding. Notice that each event may have different length.

Stream metadata

The stream metadata is a JSON file named stream.json which holds information about the stream.

Stream

A stream is a directory which contains a binary stream and the associated stream metadata file. Each stream is associated with a given part of a system. As of now, libovni can only generate streams associated to threads.