[pgrouting-users] Newbie pgr_dijkstra performance question

[Andrew Harfoot]

Hi there,

I have been looking at pgrouting in the past week, and have a test 
installation using the following:

Win7 64bit on an i7 processor with 8Gb RAM
Postgres 9.2.4 64bit
Postgis 2.0.3-2 64bit
pgrouting 2.0 64bit

My test dataset is the Ordnance Survey Meridian roads dataset for Great 
Britain which has ~1.2 million edges.

I can successfully use the pgr_dijkstra function to generate routing, 
but the performance seems a little slow. My test route takes around 10 
seconds to return in pgAdminIII, and so my first question is whether 
this is about what I should be expecting. I am not pre-filtering the 
ways being passed to pgr_dijkstra using a bounding box or such like

The second question is that whilst exploring the performance, I removed 
the indexes that pgr_createtopology had built on the source and target 
fields of the road data. To my surprise, this had no effect whatsoever 
on the performance of pgr_dijkstra, and after rebuilding them and 
looking at the index stats in pgAdminIII, this is reporting no usage of 
the indexes at all (I did rerun some routing queries after rebuilding 
the indexes!). Again, is this expected? It seems to contradict the 
recommendation to build the indexes in the pgr workshop:
http://workshop.pgrouting.org/chapters/topology.html#add-indices

Any thoughts appreciated,

Cheers,

Andy

-- 
Andy Harfoot

GeoData Institute
University of Southampton
Southampton
SO17 1BJ

Tel:  +44 (0)23 8059 2719
Fax:  +44 (0)23 8059 2849

www.geodata.soton.ac.uk