outlines the cgimap nodes flow and some hstore limitations with libpqxx

pqxxlimits.sql

CREATE TEMPORARY TABLE tmp_nodes (
id bigint primary key, 
geom geometry, -- postgis geometry
-- actually other columns as well
tags hstore);

-- nodes has the same columns and indexes as tmp_nodes, bout about 2 billion rows
INSERT INTO tmp_nodes SELECT * FROM nodes WHERE ...; -- assorted WHERE clauses
-- more inserts with joins, complicated conditions, etc

-- what I currently do

SELECT id,geom FROM tmp_nodes;
-- store the results in my C++ code

-- then loop in C++ over the results, and for each row do

SELECT (each(tags)).key as k, (each(tags)).value as v FROM tmp_nodes WHERE id=$1;

-- Then do stuff with these results

-- What I can't do due to libpqxx limitations:

SELECT id,geom,tags FROM tmp_nodes;
SELECT id,geom,hstore_to_array(tags) FROM tmp_nodes;
-- anything else involving an array