osm_mapnik=> explain analyze select * from planet_line where (tags @> 'place=>city') and name like 'a%';
                                                                  QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on planet_line  (cost=3521.71..3561.80 rows=10 width=2183) (actual time=178.296..178.296 rows=0 loops=1)
   Filter: ((tags @> '"place"=>"city"'::hstore) AND (name ~~ 'a%'::text))
   ->  BitmapAnd  (cost=3521.71..3521.71 rows=10 width=0) (actual time=178.294..178.294 rows=0 loops=1)
         ->  Bitmap Index Scan on planet_line_name  (cost=0.00..246.21 rows=10132 width=0) (actual time=0.933..0.933 rows=3458 loops=1)
               Index Cond: ((name >= 'a'::text) AND (name < 'b'::text))
         ->  Bitmap Index Scan on planet_line_tags  (cost=0.00..3275.24 rows=34285 width=0) (actual time=176.983..176.983 rows=14234 loops=1)
               Index Cond: (tags @> '"place"=>"city"'::hstore)
 Total runtime: 178.349 ms
(8 rows)

osm_mapnik=> explain analyze select * from planet_line where (tags @> 'place=>city') and (tags->'name' like 'a%');
                                                             QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on planet_line  (cost=3275.28..127271.34 rows=171 width=2183) (actual time=12685.296..12685.296 rows=0 loops=1)
   Filter: ((tags @> '"place"=>"city"'::hstore) AND ((tags -> 'name'::text) ~~ 'a%'::text))
   ->  Bitmap Index Scan on planet_line_tags  (cost=0.00..3275.24 rows=34285 width=0) (actual time=5.961..5.961 rows=14234 loops=1)
         Index Cond: (tags @> '"place"=>"city"'::hstore)
 Total runtime: 12685.367 ms
(5 rows)