[postgis-users] Configuration and performance of PostGIS
Shaozhong SHI
shishaozhong at gmail.com
Mon May 9 05:39:21 PDT 2022
Hi, Imre,
What happens if more than 1 result from the Walk the Network?
Can recursive query return all possible results?
How to handle such results?
My guess that memory allocation error occurred because that more than 1
result is found and the recursive query does not know what to do.
What is your thought?
Regards,
David
On Fri, 22 Apr 2022 at 22:14, Imre Samu <pella.samu at gmail.com> wrote:
> > as St_intersects or recursive query used,
>
> The other alternative ( ~ less efficient ) is using a “noded” network
> table ( "edge_table" )
> in the recursive query. ( and don't forget to add indexes to the
> "source" and "target" columns )
>
> WITH RECURSIVE walk_network(id, source, target, targetPoint) AS
> (SELECT et.id,et.source,et.target,ST_EndPoint(the_geom) as targetPoint
> FROM edge_table et WHERE et.id = *12*
> UNION ALL
> SELECT e.id, e.source, e.target ,ST_EndPoint(the_geom) as targetPoint
> FROM edge_table e
> , walk_network w
> WHERE w.target = e.source
> )
> SELECT ST_AsText(ST_MakeLine(targetPoint))
> FROM walk_network
> ;
> +---------------------------------+
> | st_astext |
> +---------------------------------+
> | LINESTRING(4 2,3 2,2 1,1 1,0 0) |
> +---------------------------------+
> (1 row)
>
> regards,
> Imre
>
>
> Imre Samu <pella.samu at gmail.com> ezt írta (időpont: 2022. ápr. 22., P,
> 16:39):
>
>> > With a large data set,
>>
>> :-)
>> please give more detail:
>> - How large?
>> - and what is your real "business problem"? what type of network?
>>
>>
>> > I tried to use this
>> http://blog.cleverelephant.ca/2010/07/network-walking-in-postgis.html in
>> the PostGIS.
>>
>> As I see this is a directed "network graph", and I will try using the
>> pgRouting tool - for a large graph!
>> *( "pgRouting extends the PostGIS/PostgreSQL geospatial database to
>> provide geospatial routing and other network analysis functionality." )*
>> The pgRouting project did not exist in 2010/07 when this blogpost was
>> written!
>>
>> [image: image.png]
>>
>> so I have adapted the example network ( from the original blogpost )
>> to pgRouting and this is my sample result
>>
>> ---------- ALL "downstream path" from "all deadends" sorted by descending
>> cost ---------
>>
>> +------------+-----------+---------+-------------------------------------+--------------+
>> | route_cost | start_vid | end_vid | the_geom_text
>> | edge_ids |
>>
>> +------------+-----------+---------+-------------------------------------+--------------+
>> | 6.24 | 3044 | 3000 | LINESTRING(4 4,3 4,2 3,1 2,1 1,0 0)
>> | {13,9,6,3,1} |
>> | 5.83 | 3043 | 3000 | *LINESTRING(4 3,4 2,3 2,2 1,1 1,0
>> 0) | {12,8,5,2,1} |*
>> | 4.83 | 3024 | 3000 | LINESTRING(2 4,2 3,1 2,1 1,0 0)
>> | {10,6,3,1} |
>> | 4.41 | 3014 | 3000 | LINESTRING(1 4,1 3,1 2,1 1,0 0)
>> | {11,7,3,1} |
>> | 3.41 | 3031 | 3000 | LINESTRING(3 1,2 1,1 1,0 0)
>> | {4,2,1} |
>>
>> +------------+-----------+---------+-------------------------------------+--------------+
>> and the second line is same as in the blogpost ( *"Downstream(12)" *example)
>> ,
>> just with an extra "deadends" points ; the edges :* {12,8,5,2,1} *
>>
>> start_vid : starting node/vertex id ( "deadends" in this example )
>> end_vid : ending node/vertex id constant 3000 (0,0)
>> node/vertex id = 3000 + X*10+Y coordinate // ( 2,1 ) --> 3021 ; (0,0)
>> --> 3000
>>
>>
>> > Whenever geospatial functions such as St_intersects or recursive query
>> used,
>>
>> IMHO: A good scalable data model is extremely important.
>> pgRouting has 2 important (separated) steps.
>> - creating a routing topology - route optimized database ( with "start"
>> - and "end" node/vertex )
>> - fast routing/graph/"network-walking" functions - without the geometry
>> ( using Boost Graph c++ library )
>> ( in this example I have used
>> https://docs.pgrouting.org/3.3/en/pgr_dijkstra.html )
>>
>>
>> and this is my adapted "routing" topology edge table :
>>
>> DROP TABLE IF EXISTS edge_table CASCADE;
>> CREATE TABLE edge_table (
>> id bigint primary key,
>> source bigint,
>> target bigint,
>> cost float,
>> reverse_cost float,
>> the_geom geometry
>> );
>> -- network example from
>> --
>> http://blog.cleverelephant.ca/2010/07/network-walking-in-postgis.html
>> INSERT INTO edge_table VALUES( 1, 3011, 3000, 1, -1, 'LINESTRING(1 1, 0
>> 0)');
>> INSERT INTO edge_table VALUES( 2, 3021, 3011, 1, -1, 'LINESTRING(2 1, 1
>> 1)');
>> INSERT INTO edge_table VALUES( 3, 3012, 3011, 1, -1, 'LINESTRING(1 2, 1
>> 1)');
>> INSERT INTO edge_table VALUES( 4, 3031, 3021, 1, -1, 'LINESTRING(3 1, 2
>> 1)');
>> INSERT INTO edge_table VALUES( 5, 3032, 3021, 1, -1, 'LINESTRING(3 2, 2
>> 1)');
>> INSERT INTO edge_table VALUES( 6, 3023, 3012, 1, -1, 'LINESTRING(2 3, 1
>> 2)');
>> INSERT INTO edge_table VALUES( 7, 3013, 3012, 1, -1, 'LINESTRING(1 3, 1
>> 2)');
>> INSERT INTO edge_table VALUES( 8, 3042, 3032, 1, -1, 'LINESTRING(4 2, 3
>> 2)');
>> INSERT INTO edge_table VALUES( 9, 3034, 3023, 1, -1, 'LINESTRING(3 4, 2
>> 3)');
>> INSERT INTO edge_table VALUES(10, 3024, 3023, 1, -1, 'LINESTRING(2 4, 2
>> 3)');
>> INSERT INTO edge_table VALUES(11, 3014, 3013, 1, -1, 'LINESTRING(1 4, 1
>> 3)');
>> INSERT INTO edge_table VALUES(12, 3043, 3042, 1, -1, 'LINESTRING(4 3, 4
>> 2)');
>> INSERT INTO edge_table VALUES(13, 3044, 3034, 1, -1, 'LINESTRING(4 4, 3
>> 4)');
>>
>> full example code - with data&code:
>> https://gist.github.com/ImreSamu/efda6093b67391a0edafff39d8056cb5
>>
>> if you are interested in more examples.. check the pgRouting tutorial
>> for example: *"Pre-processing waterways data"*
>>
>> https://workshop.pgrouting.org/2.7/en/un_sdg/sdg11-cities.html#pre-processing-waterways-data
>>
>> regards,
>> Imre
>>
>>
>> Shaozhong SHI <shishaozhong at gmail.com> ezt írta (időpont: 2022. ápr.
>> 22., P, 1:22):
>>
>>> Whenever geospatial functions such as St_intersects or recursive query
>>> used, the PostGIS appears to spawn away to many child queries and just
>>> obliterate the CPU. Nothing finishes.
>>>
>>> That forced me to try out to do the some tasks on the FME server.
>>>
>>> I tried to use this http://blog.cleverelephant.ca/2010/07/network
>>> -walking-in-postgis.html in the PostGIS.
>>>
>>> I tried to linecombiner in FME. LineCombiner | FME (safe.com)
>>> <https://www.safe.com/transformers/line-combiner/>.
>>>
>>> With a large data set, the running of processors were monitored. It was
>>> estimated the PostGIS one would take 16 days to complete.
>>>
>>> But, it only took a few minute to do the same thing in FME.
>>>
>>> This suggests that something is not right with the PostGIS Server.
>>>
>>> Have anyone got experience with configuration and improving perfomance
>>> of PostGIS Server?
>>>
>>> Regards,
>>>
>>> David
>>> _______________________________________________
>>> postgis-users mailing list
>>> postgis-users at lists.osgeo.org
>>> https://lists.osgeo.org/mailman/listinfo/postgis-users
>>>
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