What is the CERN Accelerator Logging Service?
The CERN-wide Accelerator Logging Service was born out of the LHC Logging Project, which was launched in 2001. The service first became operational in late 2003, and has since become what is considered to be a mission-critical service. The current mandate can be summarized as:
• Information management for Accelerator performance improvement.
• Meet INB* requirements for recording beam history.
• Make available long-term statistics for management.
• Avoid duplicate logging efforts
The logging service persists data of close to 1 million pre-defined signals coming from heterogeneous sources. These signals range from data related to core infrastructure such as electricity, to industrial data such as cryogenics and vacuum, to beam related data such as beam positions, currents, losses, etc.
The logging service provides access to logged data for more than 700 registered individuals, >100 registered custom applications from around CERN, and even offsite access for purposes such as the CNGS experiments in Gran Sasso Italy.
How is the CERN Accelerator Logging Service made?
Data is persisted in Oracle RAC databases, via a custom Java data-loading infrastructure. Approximately 2TB of data per week are written to the short-term measurement database (MDB) and around 1TB or data per week is stored online in the long-term logging database (LDB).
Data extraction is performed using a Java API, and optionally a generic Graphical User Interface (called TIMBER) to visualize the data. The entire Java infrastructure is based on the Spring framework, and pure JDBC for database interactions.
PL/SQL is extensively used for a variety of operations, including filtering and transfer of data from the short-term to long-term database.
The entire stack is heavily instrumented, in order to support the philosophy of knowing: who, is doing what, from where, and how long things take. Collectively this information is used to ensure the stability and scalability of the service in spite of ever-increasing demands.