“…Nowadays, online service systems, such as online shopping, Ebank, and search engines, have become an indispensable part in our daily life. Although tremendous efforts have been devoted to software service maintenance (e.g., collecting various monitoring data for a service system such as metrics [44,46,54], logs [19,31,51], traces [55], and alerts [29]), due to their large scale and complexity, incidents (i.e., unplanned interruption/outage to a service [2, 16,25]) are still inevitable, which could lead to system unavailability and huge economic loss [32]. For example, according to a recent survey [1], the average cost per hour of server downtime is between $301,000 and $400,000.…”