Wednesday, March 12, 2014

Parallel Database - Intraquery Parallelism

Intraquery Parallelism

It is about executing a single query in parallel using multiple processors or disks. This can be done by dividing the data into many smaller units and execute the query on those smaller tables. We have so many queries which are complex and consume more time and resources. For example, consider the query given below;
SELECT * FROM Email ORDER BY Start_Date;
This query will sort the records of Email table in ascending order on the attribute Start_Date. Assume that the Email table has 10000 records. To sort the table we need at least 10000 comparisons of Salary attribute values, if the query is executed in single processor. If the same query is executed in several processors simultaneously, we can finish sorting in lesser time. For example, if 10000 records are distributed equally into 10 processors, 1000 each, then every processor can sort 1000 records in lesser time, later it can be combined/merged using other algorithms to produce final sorted result.
In Intraquery Parallelism, we have two types;

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