SPRAY simulations may take quite a long time. You can increase the computational speed by adding the power of several PCs that work together on a SPRAY calculation.

What you need for SPRAY distributed computing is

•several PCs connected by a network

•a common network folder (all PCs must be able to write and read from this folder)

•SPRAY installations on all PCs (the minimal installation without database, tools and help files is sufficient)

•the NIGHTSHIFT tool running on every PC (this program is installed with SPRAY)

•one 'master' PC which runs SPRAY as distributed computing server.

How it works

On the master PC you load the SPRAY configuration that you want to process. You can start the distributed computing run either by hand or by OLE automation. SPRAY on the master PC divides the computational work into several tasks which are stored in a subfolder named 'untouched' of the common network folder. Thereafter it waits for incoming results in the subfolder 'results' which are added up to the total solution. If the results for all tasks have been received the simulation is ready.

The NIGHTSHIFT tools on the client PCs constantly scan the network folders for SPRAY tasks. If a task is detected, a local SPRAY program (started by OLE automation) does the computation. This activity is indicated by moving the task from the subfolder 'untouched' to the subfolder 'started'. When the computational work of the task is finished and the task is still present in the subfolder 'started', the results are stored in the subfolder 'results' and the task is deleted in the folder 'started'.

Having processed a task, NIGHTSHIFT looks for another task in the subfolder 'untouched'. If there is none, it looks for tasks in the subfolder 'started'. Work on tasks in this folder are indicated by the remark 'Working on pending tasks'.

While SPRAY computations are running on a PC you cannot use the PC for other work because it is blocked almost completely by the heavy ray-tracing workload. Hence SPRAY simulations using office PCs should be done at night. With NIGHTSHIFT options you can split a day into daytime office hours (reserved for the owner of the desktop) and night time (available for SPRAY). At daytime the normal PC operation is not disturbed by NIGHTSHIFT which is just waiting. At night all the computational power is used for SPRAY.

The algorithm described above does not require that certain client PCs are available for tasks. Client PCs can join or leave the distributed computing at any time. If there is no client there is no progress, if there are many the progress is fast. Only the master PC must be running all the time.

Before you try to work with distributed computing, please read the following sections about the master PC settings, the tool NIGHTSHIFT on the client PCs and strategy considerations for distributed computations. A VisualBasic demo shows how to control distributed computing from Excel.