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Parallel Query Processing - (System-wide and Query-based)
- Parallel query hinting can improve query performance on multi-processor systems through parallel processing, managed system-wide or per query.
- Auto parallel settings can be system-wide or specified using %PARALLEL in query FROM clauses.
- Some scenarios where %PARALLEL may be ignored include INSERT, UPDATE, and DELETE queries, certain functions or variables, and complex subqueries.
- Reasons for ignoring Parallel Query Processing include query complexity, database configurations, and data structure dependencies.
- Specific scenarios where %PARALLEL will not perform parallel processing include queries with TOP and ORDER BY clauses, views, customized tables, and remote data access.
- Considerations such as Adaptive Mode, AutoParallelThreshold, and sharded environments impact parallel processing in InterSystems IRIS, with examples provided.
- Performance tests without and with %PARALLEL hinting show varying execution times for different query types in IRIS.
- Examples illustrating usage of %PARALLEL in embedded SQL and dynamic SQL demonstrate its impact on query execution times.
- Key considerations for effective utilization of %PARALLEL in InterSystems IRIS include system settings, query structure, and optimization thresholds.
- Configurable options like AutoParallelThreshold and Adaptive Mode influence the application of parallel processing in SQL queries.
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