influxdb/query/docs/Executor.md

Executor Design

This document lays out the design of the executor.

Interface

The Executor interface is defined as:

type Executor interface {
    Execute(context.Context, Plan) ([]Result, ErrorState)
}

The executor is responsible for taking a specific plan from the Planner and executing it to produce the result which is a list of Results will allow for streaming of the various results to a client.

Concepts

The executor interacts with many different systems and has its own internal systems Below is a list of concepts within the executor.

Concept	Description
Bounded Data	Datasets that are finite, in other words batch data.
Unbounded Data	Datasets that have no know end, or are infinite, in other words stream data.
Event time	The time the event actually occurred.
Processing time	The time the event is processed. This time may be completely out of order with respect to its event time and the event time of other events with similar processing time.
Watermarks	Watermarks communicate the lag between event time and processing time. Watermarks define a bound on the event time of data that has been observed.
Triggers	Triggers communicate when data should be materialized.
Accumulation	Accumulation defines how different results from events of the same window can be combined into a single result.
Dataset	A set of data produced from a transformation. The dataset is resilient because its lineage and watermarks are known, therfore it can be recreated in the event of loss.
Block	A subset of a dataset. Row represent series and columns represent time.
Transformation	Performs a transformation on data received from a parent dataset and writes results to a child dataset.
Execution State	Execution state tracks the state of an execution.

Execution State

While both queries and plans are specifications the execution state encapsulates the implementation and state of executing a query.