Hi,
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
