Optimize the database performance

Hi,

I've a postgres 9.1 database used for map generating ( tiles ).
The system has 24Go RAM and 5 processors.
I'm using geoserver to generate the tiles.

My data used 8486 MB => psql -d gis -c "SELECT
pg_size_pretty(pg_database_size('gis'))"

I've carefully indexes the table by the "the_geom" column.

Here is my database config :

--> change :
--> listen_addresses = '*'
--> max_connections = 50
--> tcp_keepalives_idle = 60 # TCP_KEEPIDLE, in seconds;
--> shared_buffers = 1024MB # 10% of available RAM
--> work_mem = 256MB # min 64kB
--> maintenance_work_mem = 256MB # min 1MB
--> effective_cache_size = 5120MB
--> autovacuum = off

sudo nano /etc/sysctl.conf
--> kernel.shmmax=5368709120
--> kernel.shmall=5368709120

I wanted to have your opinion about this config ? What can I do to optimize
the performance ?

Thank you,