QuerySpaces on Hadoop for the ATLAS EventIndex

Hadoop-based implementation of the adaptive query engine serving as the back-end for the ATLAS EventIndex. The QuerySpaces implementation handles both original data and search results providing fast and efficient mechanisms for new user queries using already accumulated knowledge for optimisation. Detailed description and statistics about user requests are collected in HBase tables and HDFS files. Requests are associated to their results and a graph of relations between them is created to be used to find the most efficient way of providing answers to new requests The environment is completely transparent to users and is accessible over several command-line interfaces, a Web Service and a programming API.