When you run a session on a grid, the master service process runs the workflow and workflow tasks, including the Scheduler. Because it runs on the master service process node, the Scheduler uses the date and time for the master service process node to start scheduled workflows. The Load Balancer distributes Command tasks as it does when you run a workflow on a grid. In addition, when the Load Balancer dispatches a Session task, it distributes the session threads to separate DTM processes.
The master service process starts a temporary preparer DTM process that fetches the session and prepares it to run. After the preparer DTM process prepares the session, it acts as the master DTM process, which monitors the DTM processes running on other nodes.
The worker service processes start the worker DTM processes on other nodes. The worker DTM runs the session. Multiple worker DTM processes running on a node might be running multiple sessions or multiple partition groups from a single session depending on the session configuration.
For example, you run a workflow on a grid that contains one Session task and one Command task. You also configure the session to run on the grid.
The following figure shows the service process and DTM distribution when you run a session on a grid on three nodes:
When the PowerCenter Integration Service process runs the session on a grid, it performs the following tasks:
On Node 1, the master service process runs workflow tasks. It also starts a temporary preparer DTM process, which becomes the master DTM process. The Load Balancer dispatches the Command task and session threads to nodes in the grid.
On Node 2, the worker service process runs the Command task and starts the worker DTM processes that run the session threads.
On Node 3, the worker service process starts the worker DTM processes that run the session threads.