mysql innodb_buffer_pool_size let me understand
If your mysql is on dedicated server then you can set the buffer pool to the value 4GB. Initially the queries will run little slow because they require disk seeks. As your data set is very small so you can keep most of the data in memory. Once the data is present in memory performance will increase.

As your server is having huge number of reads and less number of writes good buffer pool will give better results. You can allocate around 70% memory to mysql in dedicated setup.

In crease you Key_buffer_size if you have any myisam tables. Increase the value for the below variable to avoid disk based temporary tables.

max_heap_table_size = 64M 
tmp_table_size = 64M


Dont change any on session variables they will consume more memory and may decrease the performance. Below are the session level variables for which defaults works better to most work loads.

sort_buffer_size
join_buffer_size
read_buffer_size
read_rnd_buffer_size


If you data not change frequently then enable query cache.

query_cache_size = 256M
query_cache_type = ON
query_cache_wlock_invalidate = ON ( to get accurate data )
query_cache_limit = 10M


Increasing innodb_log_buffer_size and innodb_log_file_size may help to gain the performance. But be careful if you increase the file size, it will increase the recovery time.


  Last but not lease if you are observing performance hit with 4GB
  buffer pool try setting innodb_buffer_pool_instances=2


give it a try!

Mysql has to fetch the data from the disk and keep it in memory for the first time you have accessed the data. As buffer pool contains both index and data inside it, your query performance will increase.

You can set the log file size to the best value as described HERE.

The best further description is given in rollando.