Lifecycle Query Engine system requirements are the same as those for Rational® Engineering Lifecycle Manager; however, you should consider the expected sizes of the indexed data sets and size the server accordingly. For best query and index performance, the amount of server RAM should be at least 1.25 the byte size of the index on the hard disk drive. For example, if your index takes up 48 GB of hard disk space, the server should have at least 60 GB of RAM.
The Collaborative Lifecycle Management tools have written a variety of articles on maximizing performance that also apply to this solution. For an overview, refer to: Maximizing performance.