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NextGen Archiver Backend-API
This chapter describes the NextGen Archiver Backend API
Segment Management
The segments are used for NGA archiving. In order to keep the data manageable, NGA structures the data of each archive group into segments.

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Business Logic / Control
Endless possibilities in data processing for your projects.
- Introduction to CTRL
  An introduction to the product's own programming language Control(CTRL).
- Control Classes
  The overview of classes available in Control.
- Types of Control Functions
  An overview of the types of functions distinguished within Control.
- Control graphics
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  The CtrlExtension allows the addition of custom C++ code.
- CTRL Debugger
  You can use the CTRL debugger to debug the Control programming language. The debugger can be used via its own panel, which also enables the monitoring and setting of variable values during the execution of a script.
- SQL in CONTROL
  The database functions enable you to quickly carry out value queries on data points and elements.
- API Manager
  The WinCC OA API (Application Programming Interface) offers a number of functions adding special Managers to this process control system.
- NextGen Archiver Backend-API
  This chapter describes the NextGen Archiver Backend API
  - Architecture
    This chapter provides an overview of the NGA system architecture.
  - Backend
    Description of what is a backend.
  - Segment Management
    The segments are used for NGA archiving. In order to keep the data manageable, NGA structures the data of each archive group into segments.
  - Requirements
    Contains the requirements for the NGA Backend API.
  - Project structure
    This chapter describes the project structure of the TemplateNextGenArchBackend project (lib, exe and plugin projects as well as the dplist directory).
  - Build steps
    Build steps contains the steps Create new project and Updating third-party libraries in an existing project.
  - Work modes
    The backend can work in various modes.
  - Backend API architecture
    This chapter describes what classes you must implement to implement your backend.
  - Redundancy
    Describes the NGA redundancy.
  - Backend lifetime
    This chapter describes the backend lifetime consisting of the different steps for starting and stopping such as Create a CommonBackend instance and Get DatabaseParameters.
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Segment Management

The segments are used for NGA archiving. In order to keep the data manageable, NGA structures the data of each archive group into segments.

When data is archived using the NextGen Archiver, the underlying database(s) will use evergrowing diskspace for storing data, meta information, indexes etc. To keep this heap of data manageable, NGA structures data of each archive group into segments. Each segment has a start and end time, which are determined by the group setting.

The term "segment" is an artificial term used by the NGA and is implemented differently, depending on underlying database technology. InfluxDB® implements segments as so-called "shards" whereas in Oracle "tablespaces" are used for the same purpose.

During the life cycle, each segment can change its state several times. The following states are defined:

Current: The segment exists and is currently used to store data. There is always exactly one segment with state Current. In some special cases this rule must not apply.
Online: Segment is present locally and available for read and write operations for data belonging to this timerange in the past.
Backed up: Segment is present locally and available for read operations.
Online and Backed up: Segment is present locally and available for read operations. It will automatically be deleted when the deletion parameters ("age") apply. You can write to the segment in this state by discarding the backup and making it back to "Online".
Offline and Backed up: Segment is available at backup location but cannot be read or written. Available for restore.
Restored: Segment is present and available for read operations but will not be deleted automatically.
Deleted: Segment does not exist (not locally nor on backup location) and cannot be restored.

Figure 1. NGA segment status model including transitions

For details, see subchapter Data/Segment Management.