I am not entirely sure yet what the XXL library does and why it is important, but it felt important enough to blog about it. It seems to be a library allowing one to build custom database engines. Here’s the summary from their web site:
XXL is a Java library that contains a rich infrastructure for implementing advanced query processing functionality. The library offers low-level components like access to raw disks as well as high-level ones like a query optimizer. On the intermediate levels, XXL provides a demand-driven cursor algebra, a framework for indexing and a powerful package for supporting aggregation. The XXL project provides various packages. See the longer introduction to XXL for an explanation of the packages. The library is publicly available under GNU LGPL and comes with a full documentation.