XQueryd

XQueryd is a daemon service that provides remote execution of XQuery expressions. Intended for scalable XML data processing, it accepts queries from clients over a network protocol, executes them against one or more XML data stores, and returns results in XML or JSON formats.

The name XQueryd has appeared in several XML database projects as a component that hosts the XQuery engine; it is not the formal designation of an official standard. Implementations vary in protocol, features, and deployment model, making instances of XQueryd heterogeneous across systems.

Architecture and operation are typically client-server: a persistent process runs a query planner, optimizer, and executor. It may support query plan caching, streaming evaluation, and parallel execution. Data sources include local XML databases, remote data services, or mixed stores. The service usually provides parameter binding, result streaming, and robust error handling, along with session management and authentication.

Features commonly associated with XQueryd include support for available XQuery versions, module loading, and function or variable scoping. Some implementations offer the XQuery Update Facility for modifying data, as well as security features, transaction semantics where supported, and basic monitoring and logging. Extensibility through pluggable data source adapters and indexing strategies is also typical.

Administration and deployment are configured via files or APIs. Deployments range from single-node setups to distributed configurations behind load balancers, with scaling achieved through multi-instance coordination and query routing. Use cases typically involve analytical queries over large XML collections, data integration from heterogeneous sources, and web service composition, while limitations include protocol variability and debugging complexity in distributed environments.