[postgis-users] ERROR: array size exceeds themaximumallowed(134217727)

Paul Ramsey pramsey at cleverelephant.ca
Sun Mar 21 09:57:03 PDT 2010 

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-the-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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>> >> > > > http://postgis.refractions.net/mailman/listinfo/postgis-users
>> >> > >
>> >> > > _______________________________________________
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