为什么我的带有多个线串的9400 kb PostGIS表只在heap_blks_read和heap_blks_hit中显示17kb和41kb？

Question

This table serves GeoJSON data directly to an OpenLayers app via PHP (no GeoServer). I open the app in a browser and start panning, which requests hundreds of lines. One single pan can return 1000 kb linestring geojson according to firebug. But the heap_blks_read and heap_blks_hit never get much higher than 17kb and 41kb respectively. The query that I'm using to monitor the cache rate is below. I'm just wondering how the database is performing upon many repeated queries to my geometry table.

    CREATE OR REPLACE VIEW vw_hit_rate AS 
 SELECT pg_statio_user_tables.relname,
    pg_size_pretty(pg_statio_user_tables.heap_blks_read) AS read,
    pg_size_pretty(pg_statio_user_tables.heap_blks_hit) AS hit,
    round(pg_statio_user_tables.heap_blks_hit::numeric / (pg_statio_user_tables.heap_blks_hit + pg_statio_user_tables.heap_blks_read)::numeric, 3) AS round
   FROM pg_statio_user_tables
  WHERE pg_statio_user_tables.heap_blks_read > 0
  ORDER BY round(pg_statio_user_tables.heap_blks_hit::numeric / (pg_statio_user_tables.heap_blks_hit + pg_statio_user_tables.heap_blks_read)::numeric, 3)
 LIMIT 25;