Navneet goyal bits pilani 18 aggregation thumb rule

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Unformatted text preview: s Aggregate navigation is a form of query optimization Should be offered by DB query optimizers Intelligent Middleware 03/15/10 03/15/10 Prof. Navneet Goyal, BITS, Pilani 18 Aggregation: Thumb Rule The size of the database should not The become more than double of its original size original 03/15/10 03/15/10 Prof. Navneet Goyal, BITS, Pilani 19 Aggregates: Trade-Offs Query performance vs. Costs Costs – – – – Storing Building Maintaining Administrating Imbalance: Retail DW that collapsed under the Imbalance: weight of more that 2500 aggregates and that took more than 24 hours to refresh!!! took 03/15/10 03/15/10 Prof. Navneet Goyal, BITS, Pilani 20 Aggregates: Guidelines Set an aggregate storage limit (not more than Set double the original size of the DB) double Dynamic portfolio of aggregates that change Dynamic with changing demands Define small aggregates: 10 to 20 times smaller than the FT or aggregate on which it is based than – Monthly product sales aggregate: How many times Monthly smaller than daily product sales table? smaller If your answer is 30…you are forgiven, but you If are likely to be wrong are – Reason: Sparstiy Failure 03/15/10 03/15/10 Prof. Navneet Goyal, BITS, Pilani 21 Aggregates: Guidelines Spread aggregates: Goal should be Spread to accelerate a broad spectrum of queries queries 03/15/10 03/15/10 Prof. Navneet Goyal, BITS, Pilani 22 Aggregates: Guidelines Spread aggregates: Goal should be Spread to accelerate a broad spectrum of queries queries Figure 1 Poor use of the space allocated for aggregates. 03/15/10 03/15/10 Prof. Navneet Goyal, BITS, Pilani 23 Aggregation Figure taken from Neil Raden article (www.hiredbrains.com/artic9.html) 03/15/10 03/15/10 Prof. Navneet Goyal, BITS, Pilani 24 Aggregates Issues Which aggregates to create? How to guard against sparsity failure? sparsity How How to store them? New Fact Table approach New Level Field approach How queries are directed to appropriate How aggregates? aggregates? 03/15/10 03/15/10 Prof. Navneet Goyal, BITS, Pilani 25 A...
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This note was uploaded on 03/14/2010 for the course CSE SS ZG515 taught by Professor Naveneetgoyal during the Summer '10 term at Birla Institute of Technology & Science.

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