By 11 a.m. Wednesday, it was clear the software that's the nerve centre of Montreal's métro system was going to collapse within hours.
Société de transport de Montréal engineers thought they could avoid a meltdown, but, in the end, it happened, completely shutting all four métro lines during the lunch hour ― another in a series of disruptions that have angered transit users.
The STM tried to deal with the crowds by boosting bus service on routes near the métro network and setting up a shuttle-bus service.
"Instability in the system" had been spotted in the morning, pointing to a repeat of the glitch that paralyzed the métro for an hour in July 2012, said Dominique Lemay, head of métro operations at the Société de transport de Montréal.
The unstable server is part of the main computer system used to operate the métro. It "receives and sends information from most of the systems in the métro," Lemay said.
A software patch was put in place after the July collapse.
But in October, STM engineers realized a "more complex patch" was needed or the problem would reoccur.
That software upgrade has been in the works since October but testing is not complete and it's only scheduled to be installed in late March or early April, Lemay said.
On Wednesday morning, worried the system would melt down during the busy afternoon rush hour, the engineers scrambled to fix the software without causing an interruption.
Just before noon, the engineers decided they could resolve the problem before rush hour if they could shut down the system for 10 minutes in the early afternoon, when far fewer people would be on the métro.
Lemay gave the go-ahead, and an audio announcement alerted métro users that the network was about to shut down ― only for 10 minutes.
"Just before we were going to shut down the system, the system shut down by itself," at 12:09 p.m., Lemay said.
"One server gave bad data to the system and saturated the memory of our computers and they went down" and blocked the backup server.
That complicated matters.
"It was less under our control," Lemay said. "We needed more time (because we had to) restart all systems and make sure they were stable."
It was 1:14 p.m. ― an hour and five minutes after service stopped ― before the four métro lines were running again.
The main server was back in operation but the second, backup server ― which is shut down whenever this particular software glitch occurs ― was not rebooted on Wednesday. That was to happen after the métro shut down for the night, Lemay said.
Lemay said the STM "apologizes to customers, but the good news is that it didn't happen during rush hour. And we're pretty sure our engineers and technicians have identified all the causes of the breakdowns we've had since last year and the solutions will be in place by April."
Last year, the STM started using a sophisticated new $200-million control centre to manage the métro network.
"With the new control centre, we have much more data going through our systems," Lemay said. Recent outages are "not due to the control centre, but it's related to the amount of data that has to be managed by the computers."
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