Re: Index on columns that have total of more than 255

Steven Hauser wrote: > > Baan is an application that runs over Informix and tries to map > its non-relational model to Informix by creating 'Hash Indexes'. > > This "hash index" is another field added to the table as a > concatination of all the parts of an index, and if it is > a large composit index the "hash index" is a very long string. > > Baan then creates an index on this "hash index" field. This > bloats the data in a table by adding these huge index fields. True. > This probably has the effect of trashing performance, index only > optimization is probably not possible. The index can be used to > find the row of data, and any field has to be pried loose from > data pages, not read off of indexes pages. Index reads are possible because of the way Baan read the data. If you tune OnLine as a relational database, then the performance is definitely not good. You have to tune to the way Baan see the database, then performance is not bad. > Another pitiful application built on a non-relational model is SAP. > What horrible things do they do to the supporting RDBMS can > only be imagined, but I heard they drag down performance too. Probably. Cheers, -- Mark. +----------------------------------------------------------+-----------+ |Mark D. Stock - Informix SA http://www.informix.com |//////// /| |mailto:mdstock@informix.com FAQ http://www.iiug.org |///// / //| | +-----------------------------------+//// / ///| | Tel: +27 11 807 0313 |If it's slow, the users complain. |/// / ////| | Fax: +27 11 807 2594 |If it's fast, the users keep quiet.|// / /////| |Cell: +27 83 250 2325 |Therefore, "No news: travels fast"!|/ ////////| +----------------------+-----------------------------------+-----------+