  System logs are some of the most important information for the maintenance of
software systems, which have become larger and more complex in recent years.
The goal of log-based anomaly detection is to automatically detect system
anomalies by analyzing the large number of logs generated in a short period of
time, which is a critical challenge in the real world. Previous studies have
used a log parser to extract templates from unstructured log data and detect
anomalies on the basis of patterns of the template occurrences. These methods
have limitations for logs with unknown templates. Furthermore, since most log
anomalies are known to be point anomalies rather than contextual anomalies,
detection methods based on occurrence patterns can cause unnecessary delays in
detection. In this paper, we propose LogELECTRA, a new log anomaly detection
model that analyzes a single line of log messages more deeply on the basis of
self-supervised anomaly detection. LogELECTRA specializes in detecting log
anomalies as point anomalies by applying ELECTRA, a natural language processing
model, to analyze the semantics of a single line of log messages. LogELECTRA
outperformed existing state-of-the-art methods in experiments on the public
benchmark log datasets BGL, Sprit, and Thunderbird.
