National-scale digital identity systems present unprecedented challenges in managing petabyte-scale biometric data for billion-user populations while maintaining sub-second authentication latency requirements. Traditional monolithic database architectures demonstrate fundamental limitations when confronted with heterogeneous identity data types that exhibit dramatically different structural characteristics and access patterns. This article introduces a Hybrid Polyglot Persistence architecture that strategically decouples biometric templates and demographic data across specialized storage technologies. The architecture utilizes Apache HBase for distributed biometric template storage and optimized relational databases for structured demographic information management. Performance evaluation of a production deployment serving a billion-resident population demonstrates the architecture's effectiveness in achieving consistent sub-second response times across diverse authentication scenarios. The hybrid architecture significantly outperforms monolithic alternatives while providing linear scalability characteristics that accommodate continued user population growth. Cost-benefit evaluation reveals compelling economic advantages through improved resource utilization efficiency and enhanced system availability metrics. The article establishes new architectural patterns for large-scale identity systems and provides practical implementation guidance for organizations deploying national-scale digital identity infrastructure.