Question

I am using Myisam only Database. I want to load all the indexes into cache as suggested on this page.

http://dev.mysql.com/doc/refman/5.0/en/load-index.html

How do I know if the memory allocation is sufficient to hold the key cache files?

Answer 1

MyISAM engine does this by default. There is one default default buffer, you can create additional ones and force loading of them with mentioned command (this may be useful if you want to allocate more than 4GB for key buffering).
As for default, you allocate memory for key buffering using key_buffer_size option in config file.

You can monitor usage of key buffering with SHOW STATUS and SHOW VARIABLES. The values interesting for you will be:

key_reads
key_reads_requests
key_blocks_unused
key_cache_block_size
key_buffer_size