What happened in the leap second in 2015? 2,000 network outages may cause financial market catastrophe in leap seconds

On Wednesday, July 1, the global clock adds one second to the time, which is what we call a leap second. This extra "1 second" was added at midnight on June 30th. Since Beijing is in the Eastern Eighth Time Zone, it is added 1 second after 7:59:59 on July 1, so there is a special phenomenon of 7:59:60 today. It is reported that this is the 26th increase in leap seconds since the introduction of leap seconds in 1972. The closest leap second to us was in 2012.

Why 1 second more? Due to geological processes such as tides, the Earth's rotation speed is not constant. Every once in a while, the current worldwide Coordinated Universal Time (UTC) deviates slightly from Mean Solar Time and Universal Time (UT1), which are calculated based on the Earth's motion around the Sun. Therefore, it is necessary to increase or decrease the UTC by one second to eliminate this deviation.

Leap seconds will not affect our daily lives, but it will affect the Internet. Leap seconds have reportedly caused network outages in many parts of the world, but these networks have been able to restore service quickly. Doug Madory, director of Internet analytics at network performance management firm Dyn, said that just after midnight UTC, about 2,000 networks were suddenly briefly outaged. 50% of the affected networks are located in Brazil, where ISPs use common types of routers that are not prepared for the addition of leap seconds.

Doug Madory says that most networks are restored quickly and only need to restart the router. The Internet's Global Routing Table, a distributed network database, includes 500,000 networks, so less than 0.5% of the networks are affected.

The last leap second, 2012, also had Linux system problems, some websites were down, and flights were delayed. This is only three leap seconds in the last ten years, and many developers are not familiar with this concept and do not know how to deal with it, so they do not realize the possible impact of leap seconds when writing programs that rely more on communication, which is a hidden danger. Some prominent websites and companies were affected in 2012, mostly system-level issues caused by local bugs. However, the programs that had problems and attracted attention back then can basically be considered to have fixed related bugs.

Every few years, leap seconds are added to ensure that UTC is synchronized with solar time. Due to the slowdown of the Earth's rotation, the gap between the two times increases. Since 1971, 26 leap seconds have been added. Typically, leap seconds are announced at least six months in advance to prepare IT workers. Some newly written programs with incomplete considerations may make mistakes, but most professional systems are designed with leap seconds in mind to reduce the impact of leap seconds.