2/10/2000 CHEP2000 Padova Italy The BaBar Online Databases George Zioulas SLAC For the BaBar Computing Group

2/10/2000CHEP2000 Padova Italy Overview Introduction Selection criteria Domains –Conditions –Ambient –Configuration Operational experience and future plans Summary

2/10/2000CHEP2000 Padova Italy Introduction BaBar has adopted an object oriented approach for its offline and online software OODBMS was selected for the event store Objectivity/DB is the underlying technology The Online Databases provide storage for non- event data Requirements: –Reliability –Fast storage and retrieval of data; storage of several TB

2/10/2000CHEP2000 Padova Italy Selection Criteria Support of object oriented design. C++ interface Hierarchical structure provides logical storage through persistent objects, databases and federations Application-side caching of objects retrieved from the database improves performance Autonomous partitioning and fault tolerance Distributed architecture and scalability Reuse of existing code developed by the offline system Common tools for administration, maintenance and data distribution

2/10/2000CHEP2000 Padova Italy Conditions Database Manages and tracks the Conditions of the experiment –Offline: detector calibrations, alignment etc. –Online: run information, electronic calibrations, fast monitoring Hierarchical structure Data indexed on time key Data versioning

2/10/2000CHEP2000 Padova Italy Ambient Database Provides the storage of ambient data from the Detector Controls system Design similar to Conditions Database No versioning of objects Operational information: –27 archiving processes write about 100 objects once per hour –Total size of objects about 3 MB –Storing time about 1min

2/10/2000CHEP2000 Padova Italy Ambient Data Access Ambient Database Ambient Server (C++/CORBA) Java Browser Java Browser

2/10/2000CHEP2000 Padova Italy Configuration Database Provides storage for the configuring parameters of the online system Interface to Dataflow ROMs (VxWorks) via UNIX server Configuration objects indexed on numeric keys Hierarchical tree-like structure Tree provides navigation from top, indexed by configuration key, to the subsystem configuration data on the leaves of the tree Simplifies system partitioning. Allows authorization control on subsystem level

2/10/2000CHEP2000 Padova Italy Configuration Trees

2/10/2000CHEP2000 Padova Italy Configuration Database Processes accessing the database with each configure transition: –32 Event Processing nodes –17 Detector Control processes –Dataflow server Configuration time about 15 sec

2/10/2000CHEP2000 Padova Italy Production Federation Event store PR related Conditions Configuration Conditions Ambient Configuration Prompt Reco Federation Online Federation Now Event store PR related Conditions Ambient Configuration Production Federation Comp. Building (SCS)Interaction Hall (IR2) Online PartitionPrompt Reco Partition May 99

2/10/2000CHEP2000 Padova Italy Operational Experience Running Objectivity 5.2. Many reads or one write mode System is reliable. A few hours of downtime for maintenance, upgrades 56 GB of non-event data have been recorded since May 1999 Soon to start archiving FM histograms (1GB/day) Developed own schema evolution Concurrency problems. Read locks prevent processes from writing data Sweeps between federations are tedious, time consuming

2/10/2000CHEP2000 Padova Italy Future plans Merge back the Online and Prompt Reconstruction federations Deploy the federation partitioning and fault tolerance Improve the user interface of database browsers and servers

2/10/2000CHEP2000 Padova Italy Summary The BaBar Online Databases are in use since May 1999 Problems during commissioning have been fixed System performance has been good and reliable Downtime mostly due to maintenance and upgrades Work on operational issues under way