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Real-time Query Processing

Real-time Query Processing. Roger Blake CSC 536 May 2, 2005. Real-time Query Processing - Agenda. Description of RTDBs Aspects of real-time query processing Real-time query approaches Query processing in conventional and real-time DBMS’s. Description of real-time databases.

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Real-time Query Processing

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  1. Real-time Query Processing Roger Blake CSC 536 May 2, 2005

  2. Real-time Query Processing - Agenda • Description of RTDBs • Aspects of real-time query processing • Real-time query approaches • Query processing in conventional and real-time DBMS’s

  3. Description of real-time databases • In order to be a real-time database, it needs to have: • But you already knew that…what may not have been so clear are some of the misconceptions about real-time databases… • Timing constraints (deadlines), and • Temporal data (data validity related to time)

  4. Description of real-time databases • Here are a few misconceptions about real-time databases that have persisted • Must be special purpose and highly specialized • Must be fast • Must be in-memory • There is not complete consensus, especially in practice, about what a real-time database even is

  5. Aspects of real-time query processing

  6. Real-time query approaches • Priority Memory Management (PMM) algorithm • Prioritizes queries by EDF • Queues and admits queries • Allocates memory to each query based on min/max • Adjusts memory allocations based on resource utilization

  7. Real-time query approaches • B-tree indexing for real-time queries • Starting point is a conventional B-tree with queries prioritized by EDF

  8. Real-time query approaches • B-tree indexing for real-time queries (cont’d) • As each query searches a node, it locks that node and all its child nodes for either read or write. • If there is a conflict, the query with the lowest priority restarts at the top of the tree • Rebalancing operations have the lowest priority

  9. Real-time query approaches • R-tree – similar to algorithms used for non-real-time distributed queries 4 physical locations mapped by the R-tree

  10. Real-time query approaches • R-tree adapted for real-time queries:

  11. Real-time query approaches • Freshness for base and derived real-time data • Prioritizes queries by EDF • Calculates Access Update Ratio (AUR) for each data item (access frequency / update frequency) • Uses (and adjusts) an AUR threshold for when data is updated

  12. Query processing in conventional and real-time DBMS’s • A conventional DBMS has several cross purposes with a real-time DBMS. • Multiple platforms or versions  abstraction from hardware/OS • Measured by TPC-D  performance rules • ACID properties inviolate  may be incompatible with real-time constraints

  13. Query processing in conventional and real-time DBMS’s • But conventional DBMS’s are sometimes used for data with temporal aspects, e.g. decision support systems (DSS) select city.name, sum(package.weight)from package /*real-time*/, city/*stored*/where package.weight > 100 and package.service = 'priority' and package.zip = city.zip group by city.name

  14. Query processing in conventional and real-time DBMS’s Conventional DBMS's Real-time DBMS's

  15. Real-time query processing • Algorithms have been developed for many aspects of real-time query processing • Conventional DBMS’s don’t handle real-time queries except by ‘brute force’ and possibly some of the algorithms we’ve seen • Challenges remain for real-time query processing • Security • Fault tolerance • Scalability • Generalization

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