Back in 9.2 and 9.3 there were no grid-launched workspace servers as there are in 9.4. To simulate grid-launched servers back then, the spawner-launched workspace server would spawn a grid-launched CONNECT server (a.k.a., grid server), and all code submitted to the workspace server was wrapped in a RSUBMIT and sent to the CONNECT server. To make the workspace server spawn a grid server for processing, EG added the 'Use grid if available' option.
With the advent of true grid-launched workspace servers in 9.4, the EG 'Use grid if available' is no longer needed since the workspace server itself is launched in the grid. If you use the EG 'Use grid if available' in conjunction with a grid-launched workspace server results in two grid jobs - one for the workspace server and one for the spawner CONNECT server. So in short, always use grid-launched workspace servers and do not use the EG 'Use grid if available' or 'Initialize Grid (if available)' options. Later versions of EG will detect that grid-launched workspace servers are being used and will disable the 'Use grid if available' or 'Initialize Grid (if available)' options; doing automatically what adding the EGGridPolicy/AMOGridPolicy set to Ignore does manually.
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