[Tile-serving] [osm2pgsql] Reduce memory usage of node cache (#360)

[Paul Norman]

Rerunning with this branch,

```
node cache: stored: 1484575472(54.67%), storage efficiency: 94.39% (dense blocks: 1406958, sparse nodes: 66070009), hit rate: -114.49%

Osm2pgsql took 33522s overall
52263.25user 3572.23system 9:18:42elapsed 166%CPU (0avgtext+0avgdata 16410072maxresident)k
294721152inputs+913607960outputs (78090major+4679810minor)pagefaults 0swaps
```

Basically the same overall time

---
Reply to this email directly or view it on GitHub:
https://github.com/openstreetmap/osm2pgsql/pull/360#issuecomment-117320742
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tile-serving/attachments/20150630/1213de12/attachment.html>