Ingres 9.2 Migration Guide - Actian

Sort EnhancementsQEF Sort EnhancementsQEF was improved by fine-tuning the sort algorithm, resulting in fewercomparisons between sort rows. The sort algorithm is a major consumer ofCPU time in a sort. QEF was also improved with a change that results in therows being partially sorted as they arrive in the sort.This change introduces two distinct benefits:• Duplicate rows are detected and discarded more quickly from duplicateremoval sorts (as required by “select distinct...”). This in turn increasesthe number of rows that can be processed in memory for a duplicatesremoval sort, avoiding more expensive disk sorts in many instances.• The first rows in the sort sequence can be returned before the remainingrows are completely sorted. Tests show that the first sorted row isavailable with as few as 20% of the overall comparisons required tocomplete the sort. This means that browsing or scrolling applications seethe first set of rows in less time than before.208 Migration Guide