Streaming replication performance

Hi all,

I'm testing Streamin replication with one hot standby node and I'm
experiencing high delay of hot standby node.

When I reach aprox. 50 transactions per second where every transaction
includes only simple "UPDATE status SET number = number + 1 WHERE name =
'iterations'", the standby server falls behind master and the delay is several
minutes. In comparison, Slony1 have no issues with the same test and its delay
is only several seconds.

Am I missing some configuration that affects speed of streaming replicaiton?

Both servers are connected using 1Gb network, CPU usage of both servers is
low, disk latency is not issue.

master server postgresql.conf
-----
wal_level = 'hot_standby'
vacuum_defer_cleanup_age = 10000
checkpoint_segments = 8
checkpoint_timeout = 30s
archive_mode = off
max_wal_senders = 3
wal_sender_delay = 10ms
wal_keep_segments = 128
-----

standby server postgresql.conf
-----
hot_standby = on
max_standby_streaming_delay = 30s
-----

standby server recovery.conf
-----
standby_mode = 'on'
primary_conninfo = 'host=master port=5432 user=replication2 password=password'
trigger_file = '/var/lib/postgresql/9.0/main/replica_trigger'
-----

Thank you for any advice
Antonin Faltynek