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Lab Lunch: Fabian Nagel - Recycling in Pipelined Query Evaluation

When Dec 11, 2012
from 01:00 PM to 02:00 PM
Where MF2
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Database systems typically execute queries in isolation. Sharing recurring intermediate and final results between successive query invocations is ignored or only exploited by caching final query results. The DBA is kept in the loop to make explicit sharing decisions by identifying and/or defining materialized views. Thus decisions are made only after a long time and sharing opportunities may be missed. Recycling intermediate results has been proposed as a method to make database query engines pro?t from opportunities to reuse fine-grained partial query results, that is fully autonomous and is able to continuously adapt to changes in the workload. The technique was recently revisited in the context of MonetDB, a system that by default materializes all intermediate results. Materializing intermediate results can consume significant system resources, therefore most other database systems avoid this where possible, following a pipelined query architecture instead. We show how recycling can successfully be applied in pipelined query executors, by tracking the benefit of materializing possible intermediate results and then choosing the ones making best use of a limited intermediate result cache.

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