At our busiest depot the transport office has one PC that matters more than the others. It runs the route planning software, and between two and four every afternoon the planners use it to build the next morning's runs for about sixty vehicles.
Last winter it began crashing in the middle of that work. Not every day, but three or four times a week, and nearly always after half past two. The planner lost whatever run he was building and started again, and on the worst days the plan was finished at seven in the evening and the first lorries left late the next morning.
We treated it as a fault in the PC or the software. We replaced the machine, then reinstalled the planning software, then raised it with the vendor, who found nothing in their logs and suggested more memory. Over two months we spent about thirty engineer hours on it, and the new PC crashed exactly like the old one.
An analyst who went to the depot to sit and watch finally saw it. Eleven people used that PC across three shifts, and nobody signed out. They pressed switch user, signed in as themselves and left the previous session running underneath, each with its own copy of the planning software, a browser full of tabs and an email client. By early afternoon there were often eight or nine sessions open at once. The machine had sixteen gigabytes of memory and was using all of it, and the planning software, which loads the road network for the whole region, was the program that failed when it asked for more.
So the fault was real and the software did fail. But it was a symptom of a desktop built for one person being used as a shared terminal.
That PC and the other shared machines at our depots now run as shared devices. Switch user is hidden. A session that has been disconnected for twenty minutes is signed out automatically, and the screen locks after ten minutes idle. Our monitoring now counts sessions and memory on shared machines, which we had never thought to do. The afternoon crashes stopped in the first week.
When a fault follows a machine from one box to the next, I now ask who uses it and how before I order another box.
– Serguey Shinder
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