What is a leap second? This article may help

The problem caused by this is that it generally causes the load on the server to be pushed up. It looks like livelocks on mysql and Java – the exact root cause is still being investigated but there are some articles on the web debugging as this is typed.

There are other articles to read up on here

To fix this, setting the date and time is generally advised:

date -s “`date`”
Simply restarting a service will not resolve the issue.

For those interested in avoiding this scenario you can use ntp

Mysql bug reports have been filed aswell