tailieunhanh - High-Performance Parallel Database Processing and Grid Databases- P6

High-Performance Parallel Database Processing and Grid Databases- P6: 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. | 230 Chapter 8 Parallel Universal Qualification Collection Join Queries Case 1 ARRAYS a 250 75 6 210 123 150 50 250 Case 2 SETS a 250 75 6 210 123 150 50 250 a 75 250 6 123 210 7 50 150 250 Figure Multiple hash tables collision will occur between h 150 50 25 and collection 150 50 250 . Collision will occur however if collection h is a list. The element 150 z will be hashed to hash table 1 and will collide with 150 . Subsequently the elementl50 z will go to the next available entry in hash table 1 as a result of the collision. Once the multiple hash tables have been built the probing process begins. The probing process is basicallythe cey-salpantognollection join pi 1 -ing function for collecCiya-equiioin is callsd afunction universal. ICrecorsCveOy Parallel Collection-Equi Join Algorithms 231 checks whether a collection exists in the multiple hash table and the elements belong to the same collection. Since this function acts like a universal quantifier where it checks only whether all elements in a collection exist in another collection it does not guarantee that the two collections are equal. To check for Cteeqiweity of two collections it has to check whether collection of class A collection in the multiple hash tables has reacheddie ciidol can bedone bycheckr ing whether the si calllic two matebedcollcctiensie lie shows the algorithm for thcherellclha l-liceiC ClechiiiPr r ui b Algorithm Parallel-Sort-Hash-Collection-Equi-Join step 1 disjoint partitioning Partition the objects of both classes based on their first elements for lists arrays or their minimum elements for sets bags . step 2 local joining In each procwsor for each partition a. preprocessing gsaz b s 0 sets bags only For each coliontIsi if olass4 go Sirs O Sort each sillf Oian b. hash For each cbSort of chais C Hash the ofjisoinis inOsipln iaiS babSrn c. hash and pribe For each object if sObso S Call universal 1 i g sSig gS .