Versioned Metadata Access for Snapshot-Isolated Database Schemas

The patent segments the monolithic schema lock into fine-grained locks at the catalog view level. Instead of requiring a single SCH-M lock on all schema objects, the system allows concurrent DDL operations on different catalogs by implementing separate locks for each catalog view (e.g., sys.objects, sys.columns). This segmentation enables parallel execution of DDL operations while maintaining consistency within each catalog, resolving the contradiction between schema consistency and DDL throughput.

The patent introduces catalog views as intermediaries between DDL operations and the underlying schema objects. The lock manager mediates access by allowing DDL operations to acquire locks on catalog views rather than directly on schema objects. This intermediary layer enables coordination of concurrent operations while reducing blocking, as the lock scope is limited to specific catalog views rather than the entire schema.

The patent implements dynamic lock escalation and release mechanisms. Instead of holding locks for the entire duration of query execution, the lock manager dynamically acquires and releases locks at appropriate checkpoints during DDL operations. This allows ongoing queries to complete their current operations while enabling DDL progress, reducing the overall unavailability window while maintaining consistency through controlled lock transitions.

The patent performs preliminary validation and lock acquisition attempts before fully blocking DDL operations. The system checks whether concurrent queries are using schema-affected operations and prepares lock acquisition in advance. This preliminary action allows the system to minimize blocking by only acquiring locks when necessary, reducing the unavailability window while ensuring consistency through proactive lock management.