Ingres 9.2 Migration Guide - Actian

Optimizer and Optimizedb EnhancementsOptimizer and Optimizedb EnhancementsA variety of enhancements have been made to optimizedb.The flag -zlr causes optimizedb to retain the original repetition factor whenrebuilding an existing histogram. This is useful when a histogram (and itsrepetition factor) is built once by reading the whole table, then updated laterusing sampling (which can produce inaccurate repetition factors).A minor bug was fixed to allow the “l” flag to request an exclusive lock on thedatabase during optimizedb processing (just as for other command lineutilities).The current limit of 1000 parameters coded in a separate file using the -zfparameter has been lifted. There is now no limit to the number of suchparameters.An -o filename option (similar to that in statdump) has been added tooptimizedb. It creates a statdump-style output file, which can then be inputback to optimizedb with the -i filename option. But more importantly, it doesnot update the catalog iistatistics and iihistogram tables. This allows a busyshop to construct histograms at anytime, with no worry about update conflicts.Then at a convenient later time, optimizedb can be run with the -i option toadd the histograms to the catalog.In addition to the flag enhancements, an enhancement has been introduced toallow more accurate histograms to be built on columns with significant skew intheir value sets. Specifically, a column with many distinct values, which wouldgenerate an inexact histogram, now produces exact cells for values that occursignificantly more than the average. This permits much more accurateestimates in the compilation of queries with restrictions on such columns, and,therefore, better query plans.The query compiler has been enhanced to compile more efficient strategies forcomplex queries involving aggregate views and unions.Read-only Database SupportIngres II 2.5 provides the ability to distribute a read-only database on a CD­ROM or other read-only media.Features Introduced in Ingres II 2.5 213