Configuracion de postgresql Sobre cargado

He estado leyendo sobre la configuracion de postgresql, pero tengo un
servidor que no me da el rendimiento que deveria de dar, lo monitoreo con
top, ps y pg_stat_activity y para lo que esta haciendo no deberia de ponerse
tan lento a como se pone, las tablas estan bien indexadas y se realizan
vacuum regularmente.

Las caracteristicas del servidor son:

4 Procesadores Intel Xeon Duales de 3.0Ghz
12 GB de Memoria RAM
El sistema esta operativo esta en 2 discos en RAID 1
La base de datos esta en 4 discos en RAID 5
Es un servidor dell (No recuerdo el modelo lo administro remotamente)
S.O Slackware 11.0 Linux 2.6.17.7

A alcanzado 2000 conexiones simultaneas al postgresql en max_connections le
puse 3000 para que sobrara un poco para procesos nuevos.
Tube que dividir la carga con otro servidor para que trabajara mejor y si
pues a fuerza mejoro pero por que se ahora solo alcanza a tener 500
conexiones simultaneas, pero aun asi lo sigo viendo con mucha carga.

Mi duda es mas que nada sobre la configuracion de memoria que deberia de
tener en shared_buffers y effective_cache_size.

Su ayuda se los agradeceria mucho.

En alguna pagina de internet encontre esto:

Tuning PostgreSQL for performance
2 Some basic parameters
2.1 Shared buffers

# Start at 4MB (512) for a workstation
# Medium size data set and 256-512MB available RAM: 16-32MB (2048-4096)
# Large dataset and lots of available RAM (1-4GB): 64-256MB (8192-32768)

Entonces si yo tengo 12GB de RAM es correcto que use en shared_buffers =
98304??
tambien he leido que aumentar mucho la shared_buffers alenta los procesos,
le puse 81920 se hacerca a lo correcto?? (lo multiplique por 10)

Estas son algunas seciones de configuracion del archivo postgresql.conf

#---------------------------------------------------------------------------
# FILE LOCATIONS
#---------------------------------------------------------------------------

# The default values of these variables are driven from the -D command line
# switch or PGDATA environment variable, represented here as ConfigDir.

#data_directory = 'ConfigDir' # use data in another directory
#hba_file = 'ConfigDir/pg_hba.conf' # host-based authentication file
#ident_file = 'ConfigDir/pg_ident.conf' # IDENT configuration file

# If external_pid_file is not explicitly set, no extra pid file is written.
#external_pid_file = '(none)' # write an extra pid file

#---------------------------------------------------------------------------
# CONNECTIONS AND AUTHENTICATION
#---------------------------------------------------------------------------

# - Connection Settings -

listen_addresses = '*' # what IP address(es) to listen on;
# comma-separated list of addresses;
# defaults to 'localhost', '*' = all
port = 5432
max_connections = 3000
# note: increasing max_connections costs ~400 bytes of shared memory per
# connection slot, plus lock space (see max_locks_per_transaction). You
# might also need to raise shared_buffers to support more connections.
#superuser_reserved_connections = 2
#unix_socket_directory = ''
#unix_socket_group = ''
#unix_socket_permissions = 0777 # octal
#bonjour_name = '' # defaults to the computer name

#---------------------------------------------------------------------------
# RESOURCE USAGE (except WAL)
#---------------------------------------------------------------------------

# - Memory -

shared_buffers = 81920 # min 16 or max_connections*2, 8KB each
temp_buffers = 5000 # min 100, 8KB each
max_prepared_transactions = 1000 # can be 0 or more
# note: increasing max_prepared_transactions costs ~600 bytes of shared
memory
# per transaction slot, plus lock space (see max_locks_per_transaction).
work_mem = 10240 # min 64, size in KB
maintenance_work_mem = 253952 # min 1024, size in KB
max_stack_depth = 4096 # min 100, size in KB

# - Free Space Map -

#max_fsm_pages = 20000 # min max_fsm_relations*16, 6 bytes each
#max_fsm_relations = 1000 # min 100, ~70 bytes each

# - Kernel Resource Usage -

#max_files_per_process = 1000 # min 25
#preload_libraries = ''

# - Cost-Based Vacuum Delay -

#vacuum_cost_delay = 0 # 0-1000 milliseconds
#vacuum_cost_page_hit = 1 # 0-10000 credits
#vacuum_cost_page_miss = 10 # 0-10000 credits
#vacuum_cost_page_dirty = 20 # 0-10000 credits
#vacuum_cost_limit = 200 # 0-10000 credits

# - Background writer -

#bgwriter_delay = 200 # 10-10000 milliseconds between rounds
#bgwriter_lru_percent = 1.0 # 0-100% of LRU buffers scanned/round
#bgwriter_lru_maxpages = 5 # 0-1000 buffers max written/round
#bgwriter_all_percent = 0.333 # 0-100% of all buffers scanned/round
#bgwriter_all_maxpages = 5 # 0-1000 buffers max written/round

#---------------------------------------------------------------------------
# WRITE AHEAD LOG
#---------------------------------------------------------------------------

# - Settings -

#fsync = on # turns forced synchronization on or off
#wal_sync_method = fsync # the default is the first option
# supported by the operating system:
# open_datasync
# fdatasync
# fsync
# fsync_writethrough
# open_sync
#full_page_writes = on # recover from partial page writes
#wal_buffers = 8 # min 4, 8KB each
#commit_delay = 0 # range 0-100000, in microseconds
#commit_siblings = 5 # range 1-1000

# - Checkpoints -

checkpoint_segments = 20 # in logfile segments, min 1, 16MB each
#checkpoint_timeout = 300 # range 30-3600, in seconds
#checkpoint_warning = 30 # in seconds, 0 is off

# - Archiving -

#archive_command = '' # command to use to archive a logfile
# segment

#---------------------------------------------------------------------------
# QUERY TUNING
#---------------------------------------------------------------------------

# - Planner Method Configuration -

#enable_bitmapscan = on
#enable_hashagg = on
#enable_hashjoin = on
#enable_indexscan = on
#enable_mergejoin = on
enable_nestloop = off
enable_seqscan = off
#enable_sort = on
#enable_tidscan = on

# - Planner Cost Constants -

effective_cache_size = 65536 # typically 8KB each
#random_page_cost = 4 # units are one sequential page fetch
# cost
#cpu_tuple_cost = 0.01 # (same)
#cpu_index_tuple_cost = 0.001 # (same)
#cpu_operator_cost = 0.0025 # (same)

El sysctl.conf

contiene lo siguiente:
kernel.shmmax = 970170573
kernel.shmall = 970170573
kernel.sem = 400 42000 32 1024
vm.overcommit_memory = 2

Es correcta la configuracion que tengo?
Alguna sugerencia?

Gracias de antemano....

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