The designs of high-reliabity operating systems for distributed sensor networks must take into account a wide variety of constraints: fault tolerance, performance, code size, presence of real-time tasks, maintainability, and possibly scalability. This special issue provides a forum for the presentation of high-quality, original research covering all aspects of operating systems to provide high reliability for distributed sensor networks; algorithm, design, analysis, implementation, evaluation, and case studies. Solutions might be proposed at different levels of abstractions, making use of an assortment of tools and methodologies. Flash memory is a widely used device to store data in distributed sensor nodes. Sensor nodes are highly resource constrained in terms of limited processing speed, runtime memory, persistent storage, communication bandwidth, and finite energy. Therefore, for wireless sensor networks supporting sense, store, merge, and send schemes, an energyefficient and reliable database-based query optimization technique is highly required with consideration of sensor node constraints. Databases on hard disk drives perform data storage and retrieval using index structures, which are still not practiced for sensor devices. In the first paper,