Ingres 9.2 Migration Guide - Actian

Internal Performance EnhancementsRemote Command Server EnhancementsUsers commonly encounter problems running utilities that require exclusiveaccess to the iidbdb database because the Remote Command Server process(rmcmd) keeps a session open on this database. To counter this problem,rmcmd now attaches to imadb instead of iidbdb; imadb is a system databasethat contains no historical data; it is rarely backed up and requires little or nomaintenance.Microsoft Transaction Server SupportSupport for tightly coupled XA threads and shared lock lists is now available tosupport Microsoft Transaction Server, using the ODBC 3.5 driver.Concurrent RollbackThe concurrent recovery of multiple transactions is now possible.Internal Performance EnhancementsEnhancements have been made to the internal performance that concernaggregate sort nodes, composite histograms, and optimizer support for hashjoins.Aggregate Sort NodesImprovements to aggregate handling allows Ingres to better support dataminingproducts such as CleverPath OLAP, which make extensive use of dataaggregation.Previous versions required a sort before doing grouping and aggregation.Ingres 2.6 now does grouping with hash bucketing instead of sorting. Hashgrouping is usually faster than sorting. Other internal refinements streamlinethe calculation of common aggregates, reducing the amount of CPU timeneeded.Composite HistogramsThe composite histograms enhancement allows the creation of composite ormulti-column histograms that model much more accurately the dependence ofthe values of one column on another, and lead to far better selectivityestimates and, ultimately, to better query plans.198 Migration Guide