Multiple queries in a row

Question

I have osm data imported into PostgreSQL with osm2po tool (wich makes the data routable). Also I have imported data relationed with nodes and node_tags with osmosis tool.

I need to obtain a set of nearest nodes from a given location (maybe 30 or 40). Then I need to calculate the shortest path from the given node from each others. It means to execute shortes_path query multiple times in a row, wich takes about 2 seconds (1 query 2 seconds: 30 queries 60 -> too long).

SELECT * FROM shortest_path('
   SELECT id AS id,
          source::int4 AS source,
          target::int4 AS target,
          cost::float8 AS cost
   FROM tt_2po_4pgr',
275742,
274494,
false,
false)

What would be the best way to do this in a reasonable time?

Thank in advance!

Pd: excuse my english

Edited:

In accordance to dkastl answer, I tried with wrapper functions and effectively I obtain better results 2 or 3 times better, but isn't acceptable for me yet.

With the following query:

explain analyze SELECT *
    FROM dijkstra_sp_delta('dr_2po_4pgr', 278174, 289786, 0.3);

I obtain this results: explain

Answer 1

Referring to your comment it seems to me, that you select the whole network with each query, right?

You can speedup queries if you select only the area you expect to be relevant. The easiest way to do this is to select data within a BBOX that contains start and end point of your route: http://workshop.pgrouting.org/chapters/shortest_path.html#wrapper

This will increase speed drastically for short distance queries.

Answer 2

Remember that pgrouting is not really optimised for query speed, you should use some other tools if you need real-time performance. In principle it might be possible to modify internal implementations the algorithms to calculate many routes from single point, but I suggest to check this out from pgrouting mailing list.