tailieunhanh - High-Performance Parallel Database Processing and Grid Databases- P3

High-Performance Parallel Database Processing and Grid Databases- P3: Parallel databases are database systems that are implemented on parallel computing platforms. Therefore, high-performance query processing focuses on query processing, including database queries and transactions, that makes use of parallelism techniques applied to an underlying parallel computing platform in order to achieve high performance. | 80 Chapter 4 Parallel Sort and GroupBy may also be used. Apart from these basic functions most commercial relational database management systems RDBMS also include other advanced functions such as advanced statistical functions etc. From a query processing point of view these functions take a set ofrecords . atable as their input and produce a single value as the result. GroupBy An example of a GroupBy iery is retrieve or eachdegree . The student records are. rouped uceording to specific degrees and for each group the number of records is counted. These numbers will then represent the number of students in each degree sql and a sample result of this query are given below. Query Select Sdegrhu CBUNT n From STUDENT Group By Sdegrec It is also worth menoisniny that the input table may have been filtered by using a Where clause in hothscalaraggregate and GroupBy queries and additionally for GroupBy queries theresults ofdiegroupingmay befurther filtered by using a Having clause. SERIAL EXTORNALSOnTING METHOD Serial external sortznaisextemelnrrting in a uniprocessor environment. The most common serial external sorting algorithm is based on sort-merge. The underlying principle of sort-merge algorithm is to break the file up into unsorted subfiles sort the subfiles and thedmerge the sorted subfilesinto lingerandlargeo sorted subfiles until the entire file is sorted. Note that the first stage involves sorting the first lot of subfiles whereas thesecond stage isactuaSty thu merglns phssr. Inthlsnccnanio it is important to determine thusize oithefitntioSo pubfiles thaSrretoPenorted. Normally each of thesstubffles must be pmrllenosnh tofininio the mainmsmeiy so that sorting of them tunfilut rst bhdoneipihhmemmcmorywith anymtrocil sorting technique. luoSheiwords fiiu stzeonthese nuhfilehisetualipdeSnemined by the buffer size in malnmemOT whiti in to br osscifoISOutmo mcP subtilr internally. A typicalaSgonnmifor extemet sorting .

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