Delay in MySQL Replication

[sachin chaturvedi]

Hi,
I have setup master slave replication,the replication was running fine few days ago but before few days the replication lag (seconds behind master) started buiding in.The load on the Master server as well as on Slave is under control.No queries are running on slave.
Below is the config file of Slave
[mysqld]
datadir=/data/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
query_cache_size=512M
query_cache_limit=256M
join_buffer_size=1M
thread_cache_size=4
table_cache=128
tmp_table_size=128M
max_heap_table_size=128M
max_connections=150
innodb_file_per_table
innodb_buffer_pool_size=6892M
max_allowed_packet=8M
server-id=4
relay-log=mysqld-relay-bin
[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid


Also the configration of the slave is as follows.
CPU: Intel(R) Xeon(R) CPUE5420 @ 2.50GHzserver (8 cores)
RAM : 16 GB RAM.

21:24:43 up 3 days, 2:22, 3 users, load average: 1.72, 1.87, 1.90