Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-10 Thread Mark Cave-Ayland
Tom Lane wrote: So you are saying it is de-toasted 32880 times, in this case? If not, where are the repeated de-toastings happening? Inside the index support functions. I'm thinking we could fix this by forcibly detoasting values passed as index scan keys, but it's not quite clear where's the

Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-10 Thread Mark Cave-Ayland
Tom Lane wrote: Well, yeah, because the first thing it does is pg_detoast_datum. Just as a cross-check, try changing it to copy the value without forcibly detoasting --- I'll bet it's still slow then. Yeah, that appears to be exactly the case. After some grepping through various header files

Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-09 Thread Tom Lane
Simon Riggs <[EMAIL PROTECTED]> writes: > On Mon, 2008-06-09 at 11:49 -0400, Tom Lane wrote: >> Is the value you are fetching from the geography table large enough to >> be toasted? I'm thinking you might be looking at the cost of repeated >> de-toastings. > So you are saying it is de-toasted 328

Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-09 Thread Simon Riggs
On Mon, 2008-06-09 at 11:49 -0400, Tom Lane wrote: > Mark Cave-Ayland <[EMAIL PROTECTED]> writes: > > So by adding in an extra function around the subselect result, we have > > speeded up the index lookup by several orders of magnitude, and the > > speedup appears to be coming from somewhere wit

Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-09 Thread Tom Lane
Mark Cave-Ayland <[EMAIL PROTECTED]> writes: > Tom Lane wrote: >> Is the value you are fetching from the geography table large enough to >> be toasted? I'm thinking you might be looking at the cost of repeated >> de-toastings. > Yeah, it's a fairly large geometry field so it will definitely be >

Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-09 Thread Mark Cave-Ayland
Tom Lane wrote: Is the value you are fetching from the geography table large enough to be toasted? I'm thinking you might be looking at the cost of repeated de-toastings. Yeah, it's a fairly large geometry field so it will definitely be getting toasted. So is it a case of with the mcatest fu

Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-09 Thread Tom Lane
Mark Cave-Ayland <[EMAIL PROTECTED]> writes: > So by adding in an extra function around the subselect result, we have > speeded up the index lookup by several orders of magnitude, and the > speedup appears to be coming from somewhere within the index scan?! Is the value you are fetching from the

Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-09 Thread Mark Cave-Ayland
Simon Riggs wrote: Hmmm, perhaps implicit casting? Try this to see if it works better also select count(*) from geography where centroid && (select the_geom::geometry from geography where id=69495); Hi Simon, Unfortunately that seems to take the slow runtime path too. I did initially thi

Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-09 Thread Simon Riggs
On Mon, 2008-06-09 at 14:18 +0100, Mark Cave-Ayland wrote: > Unfortunately I can't seem to work out why the extra time is > disappearing into the index scan when my extra mcatest() function is > not present, Hmmm, perhaps implicit casting? Try this to see if it works better also select count(*

Re: [HACKERS] Strange issue with GiST index scan taking far too long

2008-06-09 Thread A. Kretschmer
am Mon, dem 09.06.2008, um 14:18:50 +0100 mailte Mark Cave-Ayland folgendes: > Hi there, > > I'm currently looking at a bug report in PostGIS where we are getting > extremely long index scan times querying an index in one case, but the > same scan can take much less time if the input geometry i