Experimental Physics and
Industrial Control System

We have seen load related effects. In particular loading the gateway with arrays "freezes" the monitors on scalar
values. Recent observations with camera IOCs suggest that this is not gateway specific. Somewhere in CA monitors on
arrays seem to get higher priority than scalars. No idea where.

I’m not sure that arrays really get higher priority anywhere, but once the CA server has started to put an array value onto the wire it can’t be interrupted with updates from any other channels until every TCP packet holding that array data has been sent out. I believe (but I might be wrong) the CA gateway has a single-threaded server side, so sending a single large array through it will hold up every other channel that wants to pass through the gateway at the same time even if the two end-points are completely unrelated to the array channel.

IIRC the PVA protocol and gateway were designed to be a lot more efficient at handling large amounts of array data, which is why I would recommend using PVA for areaDetector transport.

- Andrew