Central Configuration of the Grid

TimesTen Scaleout maintains a single central configuration of the grid. This configuration is called the model. The model represents the logical topology of a grid. The model contains a set of objects that represent components of a grid, such as installations, hosts, database definitions, and instances.

You can have several different versions of the model. Each time you apply changes to the model, the grid saves the model as a version. Only one version of the model can be active in the grid at any given time.

• The latest model is the model within which you are making changes, but has not yet been applied. If you are in the process of modifying a model, then this version describes a future desired structure of a grid that only becomes the current model when you apply it.

• The current version of the model (the model that was most recently applied) always describes the current structure of the grid.

• Previous model versions describe what the grid structure used to be.

Perform the following when creating a desired structure for your grid:

1. You design the desired structure of your grid by adding or removing grid components (such as installations, hosts, and instances) to the latest model.

2. Once you complete the desired structure of a model, you apply the model to cause these changes to take effect. This version of the model becomes the current version of the model.

3. After you apply the model, TimesTen Scaleout attempts to implement the current model in the operational grid.

   It is not guaranteed that all components of the current model are running. For example, if your grid has 10 hosts configured, but only 6 of them are running at the moment, the definition of all 10 is still in the model.

Every time you use the ttGridAdmin utility to add a grid component, such as an installation, host or instance, you add model objects corresponding to these grid components to the model. Each model object specifies the attributes and relationships of the grid component.

Some model objects have relationships to other model objects. Figure 1-10 shows how the relationship is stored between model objects. That is, the host, installation and instances have a relationship where:

• The installation model object points to the host model object on which it is installed.

• Both the management instance model object and the data instance model object point to an installation model object of the installation that the instance will use and a host model object on which the instance is installed.

Figure 1-10 shows two different types of relationships between the hosts, installation, and instances that is stored within the model.

• You install a single installation on a host with one data instance, where the data instance points to the installation and to the host on which it exists.

• You create multiple data instances on a single host where they all share a single installation. Each data instance points to the same host and the same installation. The installation points to the host on which it is installed. To increase availability, avoid using multiple data instances on a single host.

Figure 1-10 Example of a Model

Description of "Figure 1-10 Example of a Model"

Any time you add or remove model objects from the model, these changes do not immediately impact a grid until you explicitly apply these changes. After you apply the changes, TimesTen Scaleout implements the current model into the operational grid. For example, if you add a new installation model object and data instance model object to the latest version of the model, applying the changes to the model performs all of the necessary operations to create and initialize both the installation and the data instance in that host.