[postgis-users] Recursive query - ERROR: invalid memory alloc request size 1073741824

[ruvenml at beamerbrooks.com]

Paul Ramsey's original example was, I would guess, intended to be the 
shortest, simplest example of using recursive functions. Adding more 
complexity to the example will just make it harder to understand.   It 
was never intended to be the basis for a full solution and has a 
fundamentally flawed architecture for that purpose; it confound toplogy 
extraction with network walking.

I would suggest to the original poster that they switch over to 
pg_routing which already has robust solutions to the problems they are 
likely to encounter.  In particular, the network walking algorithms use 
the Boost Graph C++ library are likely to execute far faster than 
anything which can be written in PL/pgSQL or python.

Ruven Brooks



On 5/8/2022 3:09 PM, Shaozhong SHI wrote:
> Hi, Imre,
>
> There is a possibility that the Walk the Network (Network Walking in 
> PostGIS · Paul Ramsey (cleverelephant.ca) 
> <http://blog.cleverelephant.ca/2010/07/network-walking-in-postgis.html?m=1&msclkid=5cf8409ecf0a11ecbbe2896397a25c2b>)  
>  encountered more than 2 answers/outputs.
>
> It may get confused and cannot finish.
>
> Can we build something in the script to report these and should there 
> be an exception, allow it to complete the task?
>
> Regards,
>
> David
>
> On Sun, 8 May 2022 at 00:59, Imre Samu <pella.samu at gmail.com> wrote:
>
>     Hi David,
>     > There is a loop of recursive query.  It runs at a point where it
>     stops.
>     >Can anyone provide pointers how to solve this problem or work around?
>
>     Please share "this" recursive query;
>
>     My guess:  Probably you have a "forever/endless loop" in your
>     data; *so you have to LIMIT the recursive part ;*
>
>     related links :
>     1.)  with limiting "depth"  ( wheredepth <1000 )
>     "Prevent infinite loop in recursive query in Postgresql"
>     https://stackoverflow.com/questions/51025607/prevent-infinite-loop-in-recursive-query-in-postgresql
>     2.)  with LIMITING clause
>     https://www.cybertec-postgresql.com/en/recursive-queries-postgresql/
>     /"This example also demonstrates how an endless loop can be
>     avoided with a LIMIT clause on the parent query."/
>
>     Regards,
>       Imre
>
>     Shaozhong SHI <shishaozhong at gmail.com> ezt írta (időpont: 2022.
>     máj. 7., Szo, 15:23):
>
>         There is a loop of recursive query.  It runs at a point where
>         it stops.
>
>         This error turned up.- ERROR:  invalid memory alloc request
>         size 1073741824
>
>         Can anyone provide pointers how to solve this problem or work
>         around?
>
>         Regards,
>
>         David
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