[postgis-users] ERROR: array size exceeds themaximumallowed(134217727)
Mike Leahy
mgleahy at alumni.uwaterloo.ca
Sun Mar 21 12:58:03 PDT 2010
Paul,
Thanks for looking into it - at least I know it's not just me (for the array
size limit at least).
What does a cleanly trapped error like this suggest to you? If you try
different variations on the where condition at the end of the statement, are
you able to get a segfault?
Mike
On Sunday 21 March 2010 12:57:03 Paul Ramsey wrote:
> As I was installing KUbuntu, I realized I should try the query on my
> own system, and under OS/X 10.6 I see the array error, though it seems
> to be cleanly trapped, there is no segfault.
>
> crashdb=# \i ./crashing.sql
> psql:./crashing.sql:36: ERROR: array size exceeds the maximum allowed
> (134217727)
> crashdb=#
>
>
> P.
>
> On Sat, Mar 20, 2010 at 9:29 PM, Mike Leahy <mgleahy at alumni.uwaterloo.ca>
wrote:
> > Leo/Regina,
> >
> > In response to your earlier message, I did find that report of the
> > identical error message. However, as I'm sure you noticed, there is no
> > apparent investigation that followed after it. That was why I went to
> > the PostgreSQL IRC channel first...they walked me through generating a
> > core dump, which is what then pointed to it being a problem related to
> > PostGIS. So while it's certainly the same error being reported, the
> > source of the problem in this case appears PostGIS-specific - likely due
> > to the logic that you note was borrowed from the array_agg that caused
> > the problem in the previous report.
> >
> > As for looking at the different query plans for working/non-working
> > versions of the statement with different where conditions, I've attached
> > several results in text files. Two examples that worked, one that
> > segfaults, and one that produces the 'array size exceeds...' error
> > message. All of these are the same query, just with variations in the
> > where condition. The query plan is a but much for me to interpret though
> > - what does this look like to the experts?
> >
> > Mike
> >
> > On Saturday 20 March 2010 23:35:32 Paragon Corporation wrote:
> >> Mike,
> >> Another thought. I suppose it could be the more or less two identical
> >> subselects both with array_aggs
> >> Just to give Paul something hopefully shorter to work with. Does this
> >> fail too?
> >>
> >> SELECT csls.chat_id, csls.ugeom
> >> FROM (
> >>
> >> SELECT '[stuff]' AS selection, st_union(geom) AS ugeom, csl1.chat_id
> >> FROM testdb.user_selections AS us1
> >> INNER JOIN testdb.chat_selection_links AS csl1 ON us1.id =
> >> csl1.selection_id
> >> WHERE (not us1.user_drawing and not csl1.deleted)
> >> GROUP BY chat_id
> >>
> >> ) AS csls
> >>
> >> LEFT JOIN (
> >>
> >> SELECT '[stuff]' AS drawing, st_union(geom) AS ugeom, csl2.chat_id
> >> FROM testdb.user_selections AS us2
> >> INNER JOIN testdb.chat_selection_links AS csl2 ON us2.id =
> >> csl2.selection_id
> >> WHERE (us2.user_drawing and us2.deleted and not csl2.deleted)
> >> GROUP BY chat_id
> >>
> >> ) AS csld ON csls.chat_id = csld.chat_id
> >>
> >> Leo and Regina,
> >> http://www.postgis.us
> >>
> >> -----Original Message-----
> >> From: postgis-users-bounces at postgis.refractions.net
> >> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
> >> Paragon Corporation
> >> Sent: Saturday, March 20, 2010 11:29 PM
> >> To: 'PostGIS Users Discussion'; mgleahy at alumni.uwaterloo.ca
> >> Subject: Re: [postgis-users] ERROR: array size exceeds
> >> themaximumallowed(134217727)
> >>
> >> Mike,
> >> Actually scanning thru the archives that 13... is a common number so
> >> suspect that is an OS limit.
> >>
> >> This could be very well a bug in PostgreSQL 8.4.
> >>
> >> Have you tried this on other PostgreSQL 8.4 installs on other your
> >> Fedoras - you mentioned trying on older installs?
> >>
> >> Your problem sounds exactly like this guy's and he wasn't using PostGIS
> >> at all but array_agg (which is logic that PostGIS borrowed from to
> >> implement the faster collecting ST_Union behavior)i
> >> http://archives.postgresql.org/pgsql-hackers/2009-06/msg01171.php
> >>
> >> If you haven't already probably good to check the plan difference
> >> between the two queries (one with addtional WHERE and one without). It
> >> could be doing something nuts like running the sub select for each
> >> record you have in the outer only when your extra WHERE condition is
> >> added and doing more or less the sane thing when you take it out.
> >>
> >> We've had some odd behavior in 8.4 with the planner doing strange things
> >> that we haven't been able to pin down and had to implement workaround
> >> for. As we described in this article.. Its probably unrelated though but
> >> just a thought to throw out at the wind.
> >>
> >> http://www.postgresonline.com/journal/index.php?/archives/149-Forcing-th
> >>e-p l anners-hand-with-set-enable_seqscan-off-WTF.html
> >>
> >> Leo and Regina,
> >> http://www.postgis.us
> >>
> >> -----Original Message-----
> >> From: postgis-users-bounces at postgis.refractions.net
> >> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul
> >> Ramsey
> >> Sent: Saturday, March 20, 2010 8:23 PM
> >> To: mgleahy at alumni.uwaterloo.ca; PostGIS Users Discussion
> >> Subject: Re: [postgis-users] ERROR: array size exceeds the
> >> maximumallowed(134217727)
> >>
> >> Mike
> >>
> >> Well, if you can reduce it to a small db dump and query that exercises
> >> it, I can install a 64bit ubuntu VM and see if it happens here too.
> >>
> >> P
> >>
> >> On Sat, Mar 20, 2010 at 3:30 PM, Mike Leahy
> >> <mgleahy at alumni.uwaterloo.ca>
> >>
> >> wrote:
> >> > FWIW, if I remove the entire where clause at the end of the
> >> > statement, it works again (with st_union()) and is virtually
> >>
> >> instantaneous.
> >>
> >> > On Saturday 20 March 2010 18:10:38 Mike Leahy wrote:
> >> >> Hey,
> >> >>
> >> >> The query (when it works) is virtually instantaneous when I use
> >> >> st_memunion() (or when I took out part of the where clause -
> >> >> although now
> >> >> I can't even get that to work, so maybe it was just lucky). Each of
> >> >> the
> >> >> subqueries also work fine without any obvious problem.
> >> >>
> >> >> To me, it seems to be a combination of things that somehow add up to
> >> >> this limitation...I don't see what settings could affect the array
> >> >> size limit
> >> >> (in postgresql.conf). Can anyone point to a config option that
> >> >> might make
> >> >> a difference, or maybe point to another place with settings I can
> >> >> tinker
> >> >> with?
> >> >>
> >> >> Mike
> >> >>
> >> >> On Saturday 20 March 2010 17:53:24 Paragon Corporation wrote:
> >> >> > Mike,
> >> >> >
> >> >> > We apologize, didn't notice this was in a subquery and that you
> >> >> > have a
> >> >> > limit statement in your query. So we presume regardless of your
> >> >> > WHERE
> >> >> > only 26 records are being selected.
> >> >> >
> >> >> > So Paul could be right that you do have data that is hitting some
> >> >> > compiled or variable limit.
> >> >> >
> >> >> > Does running the subquery alone work or you didn't try because it
> >> >> > takes a long time?
> >> >> >
> >> >> > Thanks,
> >> >> > Leo and Regina
> >> >> > http://www.postgis.us
> >> >> >
> >> >> > -----Original Message-----
> >> >> > From: Mike Leahy [mailto:mgl.gis at gmail.com] On Behalf Of Mike Leahy
> >> >> > Sent: Saturday, March 20, 2010 2:01 PM
> >> >> > To: Paragon Corporation
> >> >> > Cc: 'PostGIS Users Discussion'
> >> >> > Subject: Re: [postgis-users] ERROR: array size exceeds the maximum
> >> >> > allowed(134217727)
> >> >> >
> >> >> > Hi Leo/Regina,
> >> >> >
> >> >> > Thanks for the suggestion. I tried adding the clause 'not geom is
> >>
> >> null'
> >>
> >> >> > to the where statement in each of the two sub-queries that have the
> >> >> > st_union(geom) functions are used, but it still segfaults.
> >> >> >
> >> >> > I also tried this on a fresh database with very little data, and it
> >> >> > doesn't seem to cause problems. But I have two databases with live
> >> >> > data where I can cause this. I have been able to pare one of these
> >> >> > down to remove personal information and reduce unnecessary data,
> >> >> > while still generating the crash with that query. Would someone
> >> >> > be interested in a dump of this db? Of course, that someone would
> >> >> > ideally be able to test this on a 64-bit (K)ubutnu system, in the
> >> >> > hopes that the problem can be replicated.
> >> >> >
> >> >> > Mike
> >> >> >
> >> >> > On Saturday 20 March 2010 11:32:35 Paragon Corporation wrote:
> >> >> > > Paul,
> >> >> > > I doubt array size limit is the issue. He said when he left the
> >> >> > > where condition out it worked. I would think it would definitely
> >> >> > > blow up in that case.
> >> >> > >
> >> >> > > Mike,
> >> >> > > The issue from before was that array aggregate functions did not
> >> >> > > handle NULLs correctly. 64-bit systems were more likely to
> >> >> > > segfault or give strange Errros in this case.
> >> >> > >
> >> >> > > To rule out that we still have some of these issues in the code
> >> >> > > base, can you add a
> >> >> > >
> >> >> > > geom IS NOT NULL
> >> >> > >
> >> >> > > Condition to your WHERE filter. If that works, then the NULL
> >> >> > > issue is probably still lurking somewhere.
> >> >> > >
> >> >> > > Leo and Regina
> >> >> > > http://www.postgis.us
> >> >> > >
> >> >> > >
> >> >> > > -----Original Message-----
> >> >> > > From: postgis-users-bounces at postgis.refractions.net
> >> >> > > [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf
> >> >> > > Of Paul Ramsey
> >> >> > > Sent: Saturday, March 20, 2010 10:56 AM
> >> >> > > To: PostGIS Users Discussion; mgleahy at alumni.uwaterloo.ca
> >> >> > > Subject: Re: [postgis-users] ERROR: array size exceeds the
> >> >> > > maximum
> >> >> > > allowed(134217727)
> >> >> > >
> >> >> > > Actually, memunion does the opposite, it passes the resultant and
> >> >> > > preserves mem. The default behavior is fast-but-memory-hungry.
> >> >> > > And has been for some time, though in different forms. There were
> >> >> > > some bugs in the array handling code, but Mark CA killed most of
> >> >> > > them, so the latest 1.5 and 1.4 streams should be good. If it's
> >> >> > > possible that the issue is one of array size, maybe Mike could
> >> >> > > find the dial that controls that maximum, and turn it up and down
> >> >> > > and see if it makes his
> >> >> >
> >> >> > problem go away/happen sooner.
> >> >> >
> >> >> > > P.
> >> >> > >
> >> >> > > On Sat, Mar 20, 2010 at 7:41 AM, strk <strk at keybit.net> wrote:
> >> >> > > > On Sat, Mar 20, 2010 at 05:49:42AM -0400, Mike Leahy wrote:
> >> >> > > >> Hello again,
> >> >> > > >>
> >> >> > > >> It might be of interest to point out that substituting
> >> >> > > >> st_union() with
> >> >> > > >> st_memunion() seems to have worked around this. I'm curious
> >> >> > > >> though, because there is not a great deal of data being
> >> >> > > >> processed, and I am running this on a fairly sturdy system
> >> >> > > >> that that has more capacity than some of the Fedora systems
> >> >> > > >> I'm
> >>
> >> running.
> >>
> >> >> > > > st_memunion builds a big array with all geometries in it..
> >> >> > > > you were hitting a limit of the array type.
> >> >> > > > st_union should behave better.
> >> >> > > >
> >> >> > > > --strk;
> >> >> > > >
> >> >> > > > () Free GIS & Flash consultant/developer
> >> >> > > > /\ http://strk.keybit.net/services.html
> >> >> > > > _______________________________________________
> >> >> > > > postgis-users mailing list
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> >> >> > >
> >> >> > > _______________________________________________
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