Re: [HACKERS] Hypothetical Indexes
Hello Josh, I will take a look at pgFoundry and register a new project for index selection. I will also look for other projects there that we may help somehow. About the tutorial, I will send you the presentation we used to generate the web pages so that you can see it with OpenOffice. ;) Thanks for your feedback, Marcos. On Wed, 13 Oct 2004 11:13:55 -0700, Josh Berkus [EMAIL PROTECTED] wrote: Marcos, http://www.inf.puc-rio.br/~postgresql/ There you will find a link to a tutorial based description of the hypothetical indexes feature we have implemented on PostgreSQL 7.4 beta 3. I would love to see this as an add-in project on pgFoundry. Particularly since your online tutorial only works in Internet Explorer, so I can't read it. I believe that there was/is a team exploring a set of utilities to produce database optimization hints for the admin. Your idea would dovetail nicely with that. -- --Josh Josh Berkus Aglio Database Solutions San Francisco ---(end of broadcast)--- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
Re: [HACKERS] Hypothetical Indexes
Tom, This would be of some value if the optimizer's cost estimates were highly reliable, but unfortunately they are far from being so :-( Without the ability to measure *actual* as opposed to estimated costs, I'm not sure you can really do much. In fact, any index selection tool that uses hypothetical indexes will not recommend indexes that the optimizer does not recognize as good enough for the query. The bright side of this is that the better the optimizer gets, the better are the recommendations made by the index selection tool. And people tend to invest resources in constructing good query optimizers. Other index selection tools, such as Microsoft's and IBM's, have the same limitation. Even though, the tools are useful for people that have to deal with databases with a big quantity of tables and queries. Finding useful indexes in this kind of setting is a difficult problem for DBAs. So, our point is that hypothetical indexes just have to be as well estimated by the optimizer as conventional, real indexes. An index not suggested by the optimizer might still be usable, but that would require rewriting the query or using hints, things that need the intervention of a more skilled DBA anyway. Best regards, Marcos. regards, tom lane ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
[HACKERS] Hypothetical Indexes
Hello, I have just finished my M.Sc. thesis at Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Brazil, and we have developed a research prototype for automatic index selection using a software agent in PostgreSQL. In order to make index selection possible, we have extended the PostgreSQL DBMS to allow the simulation of hypothetical indexes. We believe these server extensions may be of value for addition to the PostgreSQL code base. A description of the work we have been doing is available at: http://www.inf.puc-rio.br/~postgresql/ There you will find a link to a tutorial based description of the hypothetical indexes feature we have implemented on PostgreSQL 7.4 beta 3. I am aware that we shouldn't go on working on things that are not on the TODO list, but we had a research oriented focus. At the end of the day, it turned out that some of the things we coded might be useful to the PostgreSQL community and we would be happy if we can contribute. So, what do you people think? Should we work together to make this new feature available on newer PostgreSQL versions? Thanks in advance for your attention, Marcos Salles. P.S: An interesting consequence of having hypothetical indexes in the system is that this eases the implementation of index tuning tools (e.g. the Microsoft SQL Server's Index Tuning Wizard). We are planning to implement one such tool to the PostgreSQL database (at first as a command-line utility). ---(end of broadcast)--- TIP 9: the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
