When you have 100,000 posts, your WordPress will be running so slow. Tuning MySQL with the following parameters will speed it up.

1, Login in MySQL with your secret password

mysql -uroot -p

2, Show parameters using MySQL command: SHOW VARIABLES;

3, Edit file: /etc/my.cnf

4, Change parameters:

key_buffer = 384M
key_buffer_size=64M
max_allowed_packet = 32M
table_cache=1024
sort_buffer_size = 8M
read_buffer_size = 2M
read_rnd_buffer_size = 8M
myisam_sort_buffer_size = 64M
thread_cache_size = 8
query_cache_size= 128M
query_cache_limit=2M
# Try number of CPU’s*2 for thread_concurrency
thread_concurrency = 4
join_buffer_size=1M

5, Restart MySQL

/etc/rc.d/init.d/mysqld restart

Reference: InnoDB vs MyISAM vs Falcon benchmarks - part 1