Обсуждение: Raising the geqo_threshold default
-----BEGIN PGP SIGNED MESSAGE----- Hash: RIPEMD160 Is there any chance we can raise the default geqo_threshold from its current default of 12? This seems too low, as a modern Postgres on modern hardware has no problem with 12 table joins. However, I have seen geqo causing trouble for clients when they hit 12 and get random (and crappy) query plans. Is the value of 12 based on any recent measurements? Thanks. - -- Greg Sabino Mullane greg@turnstep.com End Point Corporation PGP Key: 0x14964AC8 200911162121 http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8 -----BEGIN PGP SIGNATURE----- iEYEAREDAAYFAksCCN8ACgkQvJuQZxSWSsihOwCgyRldD/QS63rQzcBO6ZoyI/zH NPUAoNmkgf3Txr/V6p2oZJ/tNY8gx/mt =u1ut -----END PGP SIGNATURE-----
"Greg Sabino Mullane" <greg@turnstep.com> writes: > Is there any chance we can raise the default geqo_threshold from > its current default of 12? We were over that just a few months ago. regards, tom lane
On Mon, Nov 16, 2009 at 10:42 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote: > "Greg Sabino Mullane" <greg@turnstep.com> writes: >> Is there any chance we can raise the default geqo_threshold from >> its current default of 12? > > We were over that just a few months ago. Yeah. I think we need to see if we can do something about the ridiculous amount of memory that the standard planner consumes for large join problems. I would like to look into this problem, too, which might be related, but have not had time: http://archives.postgresql.org/pgsql-hackers/2009-11/msg00328.php ...Robert
-----BEGIN PGP SIGNED MESSAGE----- Hash: RIPEMD160 Tom Lane replied: >> Is there any chance we can raise the default geqo_threshold from >> its current default of 12? > We were over that just a few months ago. Tom, that was a very unhelpful reply. I don't have the luxury of reading, much less remembering, every thread that has occurred on the hackers mailing list. Perhaps you mean the discussion from July 6, 2009 started by Robert Haas? That was approximately 8000 messages ago, and no consensus was reached that I could find. So I'd like to respectfully ask the hackers to consider raising the default value from 12 to 16 (as Robert Haas first suggested) or even higher (20?). Whether or not we make GEQO less random, replace it someday with something else, tweak *_collapse_limit, etc. is not as important in my mind as minimizing this unexpected foot gun for future releases. Thanks. - -- Greg Sabino Mullane greg@turnstep.com End Point Corporation PGP Key: 0x14964AC8 200911170859 http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8 -----BEGIN PGP SIGNATURE----- iEYEAREDAAYFAksCrIIACgkQvJuQZxSWSsjReACgihBX9gD+VE6kcd5gsFPjtigj xgEAoM4S4tRj/PsMEVUEM5K6taGGUWfm =2WB4 -----END PGP SIGNATURE-----
"Greg Sabino Mullane" <greg@turnstep.com> writes: > Perhaps you mean the discussion from > July 6, 2009 started by Robert Haas? That was approximately 8000 > messages ago, and no consensus was reached that I could find. Precisely. > So I'd like to respectfully ask the hackers to consider raising the > default value from 12 to 16 (as Robert Haas first suggested) or > even higher (20?). Have you got any evidence whatsoever to back up those suggestions? (In particular, evidence that it's not going to cause serious performance degradations for some people.) Otherwise you're not advancing the discussion past where it left off. regards, tom lane