Обсуждение: query optimizer
Hello,
As I see the documentation of postgres, postgres use genetic algorithm for query optimization rather than system R optimizer. right?
--
Jungmin Shin
"jungmin shin" <jungmin.shin@gmail.com> writes:
> As I see the documentation of postgres, postgres use genetic algorithm for
> query optimization rather than system R optimizer. right?
Only for queries with more than geqo_threshold relations. The join
search algorithm for smaller queries is a System-R-like dynamic
programming method.
regards, tom lane
On Tuesday 17 April 2007 Tom Lane's cat, walking on the keyboard, wrote: > "jungmin shin" <jungmin.shin@gmail.com> writes: > > As I see the documentation of postgres, postgres use genetic algorithm > > for query optimization rather than system R optimizer. right? > > Only for queries with more than geqo_threshold relations. The join > search algorithm for smaller queries is a System-R-like dynamic > programming method. > Hi, I'd like to better understand how the optimizer works and is implemented. Is there any available documentation (before start reading the source!) to understand concepts about geqo and system r? Any chance about any demo or presentation with detailed examples (about how the optimizer makes and discards choices, not about how to read the planner output)? Thanks, Luca
Luca Ferrari <fluca1978@infinito.it> writes: > I'd like to better understand how the optimizer works and is implemented. Is > there any available documentation (before start reading the source!) to > understand concepts about geqo and system r? Any chance about any demo or > presentation with detailed examples (about how the optimizer makes and > discards choices, not about how to read the planner output)? http://developer.postgresql.org/pgdocs/postgres/overview.html (particularly 42.5) src/backend/optimizer/README The developers section of the website used to have slides from a couple of talks I gave at OSCON, but I don't see them there anymore :-( regards, tom lane
On Thu, 19 Jul 2007, Tom Lane wrote: > The developers section of the website used to have slides from a couple > of talks I gave at OSCON, but I don't see them there anymore :-( This one is still around: http://conferences.oreillynet.com/presentations/os2003/lane_tom.pdf I'd also recommend http://www.gtsm.com/oscon2003/toc.html on this topic. -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
On Thu, Jul 19, 2007 at 10:41:03AM -0400, Tom Lane wrote: > Luca Ferrari <fluca1978@infinito.it> writes: > > I'd like to better understand how the optimizer works and is implemented. Is > > there any available documentation (before start reading the source!) to > > understand concepts about geqo and system r? Any chance about any demo or > > presentation with detailed examples (about how the optimizer makes and > > discards choices, not about how to read the planner output)? > > http://developer.postgresql.org/pgdocs/postgres/overview.html > (particularly 42.5) > > src/backend/optimizer/README > > The developers section of the website used to have slides from a couple > of talks I gave at OSCON, but I don't see them there anymore :-( How long ago was this (that they were on the website)? I don't recall that ever being removed, and I can't find it in the cvs either. If you still have the presentations, we can always add them back in... (I recall reading them, but don't have a local copy) //Magnus
Magnus Hagander <magnus@hagander.net> writes: > On Thu, Jul 19, 2007 at 10:41:03AM -0400, Tom Lane wrote: >> The developers section of the website used to have slides from a couple >> of talks I gave at OSCON, but I don't see them there anymore :-( > How long ago was this (that they were on the website)? I don't recall that > ever being removed, and I can't find it in the cvs either. Hmm, I thought they were once on the same page as Bruce's papers, now http://www.postgresql.org/developer/coding but possibly I'm mistaken; it was well before the website reorg anyway. > If you still have the presentations, we can always add them back in... (I > recall reading them, but don't have a local copy) Yeah, the PDFs are still in my home directory on cvs.postgresql.org. regards, tom lane
Magnus Hagander wrote: > On Thu, Jul 19, 2007 at 10:41:03AM -0400, Tom Lane wrote: > > The developers section of the website used to have slides from a couple > > of talks I gave at OSCON, but I don't see them there anymore :-( > > How long ago was this (that they were on the website)? I don't recall that > ever being removed, and I can't find it in the cvs either. > > If you still have the presentations, we can always add them back in... (I > recall reading them, but don't have a local copy) Last time I asked, I found them in Tom's home dir in cvs.postgresql.org. -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support
On Thursday 19 July 2007 Tom Lane's cat, walking on the keyboard, wrote: > http://developer.postgresql.org/pgdocs/postgres/overview.html > (particularly 42.5) I have already read this, thanks. > > src/backend/optimizer/README I've read this yesterday, very interesting, but I'm looking for something similar related to geqo. I mean, is there any presentation/demo that step-y-step explains how geqo could take decisions? Thanks, Luca
Luca Ferrari <fluca1978@infinito.it> writes: >> src/backend/optimizer/README > I've read this yesterday, very interesting, but I'm looking for something > similar related to geqo. I mean, is there any presentation/demo that > step-y-step explains how geqo could take decisions? There's not a lot, but I just made a few improvements here and here: http://developer.postgresql.org/pgdocs/postgres/planner-optimizer.html http://developer.postgresql.org/pgdocs/postgres/geqo-pg-intro.html Beyond that, the GEQO chapter provides several references, and IMHO you should not be all that resistant to looking into the source code. Even if you don't read C well, many of the files provide a wealth of info in the comments. regards, tom lane
Tom Lane wrote: > Magnus Hagander <magnus@hagander.net> writes: >> On Thu, Jul 19, 2007 at 10:41:03AM -0400, Tom Lane wrote: >>> The developers section of the website used to have slides from a couple >>> of talks I gave at OSCON, but I don't see them there anymore :-( > >> How long ago was this (that they were on the website)? I don't recall that >> ever being removed, and I can't find it in the cvs either. > > Hmm, I thought they were once on the same page as Bruce's papers, now > http://www.postgresql.org/developer/coding > but possibly I'm mistaken; it was well before the website reorg anyway. > >> If you still have the presentations, we can always add them back in... (I >> recall reading them, but don't have a local copy) > > Yeah, the PDFs are still in my home directory on cvs.postgresql.org. Added to the website, will appear on next build. //Magnus
On Saturday 21 July 2007 Tom Lane's cat, walking on the keyboard, wrote: > Beyond that, the GEQO chapter provides several references, and IMHO > you should not be all that resistant to looking into the source code. > Even if you don't read C well, many of the files provide a wealth of > info in the comments. Thanks for you integration and, even if I'm not a C-expert, I'd like to read the source code to better understand how postgres works. Nevertheless, since the source code can be very long, it should be better to have a kind of uml diagram or something similar to understand on which point of code to focus on. That's what I was looking for. Luca