Grid Processing Overview:
When a Power Center domain contains multiple nodes, you can configure workflows and sessions to run on a grid. When you run a workflow on a grid, the Integration Service runs a service process on each available node of the grid to increase performance and scalability. When you run a session on a grid, the Integration Service distributes session threads to multiple DTM processes on nodes in the grid to increase performance and scalability.
You create the grid and configure the Integration Service in the Administration Console. To run a workflow on a grid, you configure the workflow to run on the Integration Service associated with the grid. To run a session on a grid, configure the session to run on the grid.
The Integration Service distributes workflow tasks and session threads based on how you configure the workflow or session to run:
- Running workflows on a grid. The Integration Service distributes workflows across the nodes in a grid. It also distributes the Session, Command, and predefined Event-Wait tasks within workflows across the nodes in a grid.
- Running sessions on a grid. The Integration Service distributes session threads across nodes in a grid.
Note: To run workflows on a grid, you must have the Server grid option. To run sessions on a grid, you must have the Session on Grid option.
Running Workflows on a Grid:
When you run a workflow on a grid, the master service process runs the workflow and all tasks except Session, Command, and predefined Event-Wait tasks, which it may distribute to other nodes. The master service process is the Integration Service process that runs the workflow, monitors service processes running on other nodes, and runs the Load Balancer. The Scheduler runs on the master service process node, so it uses the date and time for the master service process node to start scheduled workflows.
The Load Balancer is the component of the Integration Service that dispatches Session, Command, and predefined Event-Wait tasks to the nodes in the grid. The Load Balancer distributes tasks based on node availability. If the Integration Service is configured to check resources, the Load Balancer also distributes tasks based on resource availability.
For example, a workflow contains a Session task, a Decision task, and a Command task. You specify a resource requirement for the Session task. The grid contains four nodes, and Node 4 is unavailable. The master service process runs the Start and Decision tasks. The Load Balancer distributes the Session and Command tasks to
nodes on the grid based on resource availability and node availability.
Running Sessions on a Grid:
When you run a session on a grid, the master service process runs the workflow and all tasks except Session, Command, and predefined Event-Wait tasks as it does when you run a workflow on a grid. The Scheduler runs on the master service process node, so it uses the date and time for the master service process node to start scheduled workflows. In addition, the Load Balancer distributes session threads to DTM processes running on different nodes.
When you run a session on a grid, the Load Balancer distributes session threads based on the following factors:
- Node availability :- The Load Balancer verifies which nodes are currently running, enabled, and available for task dispatch.
- Resource availability :- If the Integration Service is configured to check resources, it identifies nodes that have resources required by mapping objects in the session.
- Partitioning configuration. The Load Balancer dispatches groups of session threads to separate nodes based on the partitioning configuration.
You might want to configure a session to run on a grid when the workflow contains a session that takes a long time to run.
Grid Connectivity and Recovery
When you run a workflow or session on a grid, service processes and DTM processes run on different nodes. Network failures can cause connectivity loss between processes running on separate nodes. Services may shut down unexpectedly, or you may disable the Integration Service or service processes while a workflow or session is running. The Integration Service failover and recovery behavior in these situations depends on the service process that is disabled, shuts down, or loses connectivity. Recovery behavior also depends on the following factors:
- High availability option:-When you have high availability, workflows fail over to another node if the node or service shuts down. If you do not have high availability, you can manually restart a workflow on another node to recover it.
- Recovery strategy:- You can configure a workflow to suspend on error. You configure a recovery strategy for tasks within the workflow. When a workflow suspends, the recovery behavior depends on the recovery strategy you configure for each task in the workflow.
- Shutdown mode:- When you disable an Integration Service or service process, you can specify that the service completes, aborts, or stops processes running on the service. Behavior differs when you disable the Integration Service or you disable a service process. Behavior also differs when you disable a master service process or a worker service process. The Integration Service or service process may also shut down unexpectedly. In this case, the failover and recovery behavior depend on which service process shuts down and the configured recovery strategy.
- Running mode:-If the workflow runs on a grid, the Integration Service can recover workflows and tasks on another node. If a session runs on a grid, you cannot configure a resume recovery strategy.
- Operating mode:- If the Integration Service runs in safe mode, recovery is disabled for sessions and workflows.
Note: You cannot configure an Integration Service to fail over in safe mode if it runs on a grid.