can you halp me? Thks, Felipe----- Original Message ----- From: "Martijn van Oosterhout" <kleptog@svana.org>
To: "Felipe Rondon Rocha" <[EMAIL PROTECTED]> Sent: Tuesday, December 19, 2006 8:39 AM Subject: Re: Fw: [HACKERS] choosing use an index or not
No idea, ask on -hackers... I only know the concepts of how it works, I have no idea about the code itself. Have a nice day, On Tue, Dec 19, 2006 at 08:39:12AM -0300, Felipe Rondon Rocha wrote:
Hi Martijn,my problem is that our group of study made a modification to always use the index on a "select explain ..." statement. But as a matter of fact we found some bugs that have to be fixed. I know how the choice of an index happens. What I need to find is the moment that PostgreSQL compares the costs of all trees (paths) and decide to use the index or not. Do you have any tips?Thank you, very much. Regards, Felipe----- Original Message ----- From: "Martijn van Oosterhout" <kleptog@svana.org>To: "Felipe Rondon Rocha" <[EMAIL PROTECTED]> Cc: <pgsql-hackers@postgresql.org> Sent: Thursday, December 14, 2006 9:56 AM Subject: Re: [HACKERS] choosing use an index or not
On Thu, Dec 14, 2006 at 10:06:45AM -0300, Felipe Rondon Rocha wrote: >Hi everyone, > >Do you know in which part of the file analyze.c, PostgreSQL decides >to use or not an index? I?m making a test and I can?t trace the >moment that he makes the choice. It doesn't explicitly make the choice anywhere. The planner makes a set of "paths" that can be used. So for each table a "path" is made for a sequential scan and one or more "paths" for each index. For each a cost is calcualted and whichever has the lowest cost is the one chosen. It's quite dynamic, the choice also depends on what happens to the result. There's no point using an index if the result is in the wrong order for the join, for example. Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/>From each according to his ability. To each according to his ability to >litigate.
-- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/
From each according to his ability. To each according to his ability to litigate.
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TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
